I. THE PLANT CHEMIST J. ALFRED HALL
At the time this article was written Dr. Hall was Biochemist with the Forest Products Laboratory of the U. S . Forest Service at Madison, Wisconsin. I n 1937 he became Associate Director of the California Range and Experiment Station. He attended Earlhum College and Indiana Uninersity for a time and received the B.S., M S . , and Ph.D. degrees from the University of Wisconsin. He i s a member of the Phi Beta Kappa and
Sigma X i societies. Dr. Hall is the author of several publications on plant chemistry.
+ + + + + + It was about eight years after graduation before I discovered what kind of a chemist I was, and that happened only when I entered the Federal Civil
Service and achieved a title, dz.,Biochemist. Now that is a sufficiently broad classificationto cover almost anybody operating in the field of vital products. However, in my own case, the work has been confined to plant products. Thus, the classification might very well be plant biochemist, but it would still be erroneous in view of the fact that one works mostly with materials separated from the plant and, therefore, no longer in the sphere of vital activities. Suppose we say then, just to be on some sort of solid ground, that I am a plant chemist, primarily interested in how plants manufacture the myriad of substances which they produce. We must admit that this is a large order, especially since the groundwork of the problem is still a very rickety piece of construction. That is, we as yet know comparatively little about the actual substances, produced by the plant as end-products of their growth and next to nothing about the substances that are intermediate between the sugar of photosyntheses and the end-products. The specific problem that I am busied with is the elucidation of the chemical mechanism by which the pine trees of the southeastern states produce the oleoresin from which are obtained the turpentine and rosin of commerce. Here is the problem, briefly. The tree is wounded into the sapwood, and from the wound exudes the sticky water-insoluble oleoresin. Repeated wounding causes repeated exudation, and the process can go on almost indefinitely. Under proper conditions, a tree can be turpentined for one hundred years. In the first place, the exudation of resin from a water-filled tissue is peculiar enough, although we can see how the resin exudes from specialized passages. However, we want to know how the resin gets there, and, above all, where in the tree it is formed, and by what mechanism. There appeared to be two avenues of approach, as is usually the case in any research problem-the library and the laboratory; the library first, of course. In pine oleoresin, we are dealing with a material which contains terpenes and resin acids, both of which are produced by many plants other than the pine tree. In fact, terpenes are so widely spread in the plant kingdom that one considers them almost universal. Both groups, as well as many other compounds, are made up of a simple unit, put together in different ways to form different compounds. In fact, the general occurrence of what we choose to call isoprene polymers leads us to think that their universality is the result of a general law of plant chemistry. The only trouble is we have never found any isoprene in plants, nor do we know from what it arises. The fust fruit of library research was a clear picture of the close relationship of the whole terpene and resin acid family, and the development of a hypothesis in which these substances were derived from watersoluble precursors which in turn could be theoretically derived from sugars such as we know are formed by photosynthesis. All this was purely hypothetical and based on a thorough survey of all the recorded occurrences of these substances. Also, I was drawing some-
what on past experience in postulating water-soluble combinations for the translocation of oleoresinous substances in the plant. With this hypothesis developed, nothing remained but to attack the tissues of the pine tree and the oleoresin itself and see what could be found. Clearly, we were compelled to deal with the material separated from the tree, because in the present state of the problem, we had no knowledge with which to begin any other study. I might as well admit now that we are a long way from the solution, but there are rays of hope. In the oleoresin I found a very small quantity of a watersoluble substance with peculiar properties. It was soluble in either ether or water. I t was evidently carbohydrate in nature, and, upon hydrolysis of the very small quantity available, I found I had a glucoside decomposing into a sugar, a volatile oil, and a resin which gave a t least the color reactions of a resin acid. Now, of course, that was what I had hoped for, but the amount here was so small that i t would have cost a fortune to get enough with which to work. So I began the examination of the inner bark of the tree. This tissue contains, along with a great amount of other materials, a small amount of apparently the same glucoside, although I am not a t all ready to state that they are the same. Its isolation, and the necessity of assuring myself that I am not overlooking something else of importance compels a pretty complete analysis of the tissue. This work is yielding a considerable amount of information which will all be fitted into the picture when i t is done, we hope. In the meantime, I have started the same sort of survey on the growing tips of the tree, and have great hopes of finding this glucoside in sufficient concentration to enable a good characterization. One might ask, "What of it? Of what possible benefit to humanity will i t be if you do find out how a pine tree forms oleoresin?" Well, the problem is a bit larger than that in its application, for i t is, after all, a part of the big problem of synthesis in plant life, and thus a part of man's attempt to free himself from the trammels of his natural environment. Immediately, of course, the objective is to get better control of our vast pine forests and operate them more intelligently. To do that, we need to know all we can about what goes on in them. I spent some years in California helping develop a by-products industry from oranges and lemons. There, our limiting factor was always our lack of knowledge of the actual make-up of the fruits with which we were working. In short, we cannot know enough about our materials to get efficient management of their production. A good illustration of this point can be derived from our work on oranges in California. Specifically, it was thought that the undesirable odors developed in preserved orange juice arose from chemical changes taking place in the volatile odorous constituents of the fresh juice. It followed that we needed to know what these constituents were. I worked up about 25,000 gallons of juice and obtained about one pint of volatile
oil. After sorting out its constituents to the best of my ability, we concluded that they were not responsible, but we knew a lot more about the odor of fresh orange juice than we did before. Then there was the problem of the bitter taste that develops in certain orange juices on standing. That I was able to locate as coming from the tissue covering the pulp sections, and actually isolated a little of the bitter principle, probably impure. However, we found out enough about it to give us some control over the production of juice from these oranges. Incidentally, it was this work on orange glucosides that started the thought on the mechanism by which waterinsoluble bodies are moved through the sap of the plant, and led to the development of the hypothesis on which my present work is based. The chemist who chooses to work with plant substances along the lines indicated above will probably never run out of problems. Indeed, in spite of the thousands of substances that have been isolated from plants, the surface has hardly been scratched, and hundreds of interesting plants still await their first investigation. Hundreds of others have been examined in cursory fashion, with only those substances being obtained that were easy of access. A mere handful of plants have been subjected to anything like a complete examination. Such research, however, requires money and, except in cases of plants of known commercial importance, adequate financial support has been lacking. The young chemist, looking for a field of large financial profit, might well search elsewhere, for his rewards in plant chemistry will probably not be pecuniary. However, in the field of pharmacy, and in those technological processes directly utilizing vegetable products, there are ample opportunities for the research plant chemist. It is not often that such fields develop data of direct interest in the field of plant synthesis, but it must be remembered that all careful work in the characterization of plant substances must some day be of value in elaborating a complete theory of photosynthesis. Thus, even the routine worker in the drabbest field can contribute to the larger objective, and earn a living while satisfying his desires for research. Fortunately, the chemist well trained for careful phytochemical labors is also trained for general organic
work. Thus, as for making a living, he is doubly equipped, with the advantage that, if opportunity offers, he may combine a living with labor in a field where unrivalled opportunities for productive investigation continually challenge the patient and imaginative worker. [When Dr. Hall was asked what training and personal qualifications a plant chemist should have, he replied with the following description of an ideal phytochemist.] Let us assume that we have a healthy, industrious man, with a good brain and a healthy imagination. He must be as capable with his hands as with his head for he will need to be a bit of a carpenter, plumber, steamfitter, electrician, and laboratory man, and not afraid to get a little dirty in working. Now, if he has a highly developed bump of curiosity directed toward things of nature, and has or can develop a true sense of scientific accuracy, he is worth risking with a course leading to a Ph.D. in chemistry. L i t his training include: (1) The usual undergraduate courses in chemistry, physics, and botany. (2) All the organic he can get with emphasis on characterization and natural substances. (3) Physical chemistry. The theoretical background is desirable but not indispensable. Knowledge of the "working tools" is necessary. (4) A lot of plant physiology. The combination of thorough chemical training and plant physiology in the right man makes an irresistible combination. (5) German and French a t least, and the more languages the better.
I assume he will have a mastery of clear, concise English, for without it he is hopeless. Let him learn some economics and any others of the social sciences, for he must have a bit of altruistic social philosophy to be happy in his work. In short, in addition to the necessary technical courses listed above, educate him, if possible, in as broad a fashion as he can take, for he will need vision including fields far beyond the confines of the laboratory.
