156 



THE CELL AND PROTOPLASM 



possible to connect this polar auxin move- 

 ment with any other physical forces which 

 can be measured, such as potential differ- 

 ences (Clark 1937). But I am thoroughly 

 convinced that with the help of a really 

 competent physicist the problem can be 

 solved. And the importance of the problem 

 from a general biological viewpoint is suf- 

 ficient to justify a very thorough investi- 

 gation. 



When we conclude that organization and 

 correlation in plants is regulated by the 

 polar movement of auxin, then it will be 

 evident that this is also a complete proof 

 of Sachs' conception of correlation (1880; 

 1882). 



Another of the great biological problems, 

 the action of the genes, can be approached 

 by the student of hormones. Many genes 

 affect or determine form. Hormones are 

 the ultimate agents to affect that form. 

 Therefore either the hormones are formed 

 under the influence of the genes, or the 

 genes influence the hormones after they are 

 formed. By a close analysis of the inter- 

 action between genes, hormones, and form, 

 the gene action can be approached. I want 

 to cite only one example, the work of van 

 Overbeek (1938) on the genetic dwarfs of 

 corn. In this case he could establish the 

 fact that the different dwarf genes all in- 

 creased the oxidative activity of the cells, 

 as measured by catalase and peroxidase 

 activity. This in turn caused an increased 

 auxin destruction, so that the auxin formed 

 in the stem apex practically or completely 

 failed to reach the growing regions, and no 

 elongation of the stem could occur. There- 

 fore a dwarf was produced. This example 

 shows how it is possible to shorten by a hor- 

 mone analysis the unknown portion of the 

 chain of reactions lying between the gene 

 and its ultimate morphological effect. 



Now it becomes necessary to tie all oc- 

 casional observations on plant hormones 

 together into one composite picture of the 

 plant as a whole — as an organism — as some- 

 thing more than a simple colony of cells. 



Transplantation (Went 1938a) and other 

 experiments (Went 1938) have furnished 

 evidence for the existence of another stem 



growth factor coming from the root sys- 

 tem, which has not been chemically isolated 

 as yet, but which will be named caulocaline. 



Recently the chemical nature of some 

 factors required for leaf growth has been 

 established by Bonner and Haagen-Smit 

 (1939). These factors are necessary for 

 growth in the surface of the leaf, and are 

 produced by the older, fullgrown leaves. 

 Therefore the correlations between young 

 leaves and the rest of the plant are brought 

 about by other specific growth factors, such 

 as adenine. 



One further correlation which is caused 

 by hormones, is shown by recent experi- 

 ments on photoperiodism (Hamner and 

 Bonner 1938). It was found that the dif- 

 ferentiation of a vegetative bud into a 

 flower bud was caused by a factor coming 

 from the mature leaves. Determination of 

 the chemical nature of this flower-forming 

 substance now seems to lie well within 

 practical possibilities, since James Bonner 

 recently obtained active extracts which in- 

 duce flower formation. 



Figure 2 summarizes the different inter- 

 relations between the parts of a plant, 

 which have just been discussed. It shows 

 more clearly than any verbal description 

 the large number of correlations inside a 

 plant, all due to the action of hormones. 

 Since all these relations are quantitative, an 

 amazingly great unity within the plant is 

 realized, in order that one part shall not 

 grow too much at the expense of another. 

 Only in this way is it possible for taxono- 

 mists to describe a plant in terms of rela- 

 tive dimensions. The picture is the same 

 as for animals. 



And it also brings back our original con- 

 tention that the interrelations between cells 

 and organs can be brought about by the 

 simplest means: that certain cells lose the 

 ability to synthesize one or another simple 

 basic nucleus which is necessary for their 

 build-up. 



Summary 



An effort has been made in this discus- 

 sion to bring out especially those facts 

 which have a more direct bearing on the 



