BOTANY AND MORPHOGENESIS II9 



gation. They are less tightly organized than animals and therefore pose most 

 problems of morphogenesis in relatively simple terms. The complexity that 

 the presence of a nervous system introduces into animal development is 

 missing in plants, and the basic activities and possibilities of relatively undif- 

 ferentiated living stuff can here be studied most directly. Plants also are 

 usually more tractable than animals and easier to deal with experimentally. 

 It is therefore evident why a study of plant development has made so many 

 notable contributions to this field in the past and is so promising for a further 

 understanding of morphogenetic problems. It will be profitable in this anni- 

 versary year to examine, even very briefly, what has already been accom- 

 plished and what the possibilities are for further progress here. 



In the history of morphogenesis one often thinks first of the great names 

 in zoology — Roux, Driesch, Wilson, Morgan, and many more — who studied 

 the problems of experimental embryology so fruitfully, among amphibia 

 and various invertebrates, more than half a century ago. Let us not forget, 

 however, that Vochting, Goebel, and their colleagues at this time were laying 

 a firm foundation for morphogenesis in plants as well. Driesch's famous 

 aphorism, "The fate of a cell is a function of its position," which states so 

 compactly the essence of the phenomenon of organization, was uttered about 

 the turn of the century, but one can find almost these same words in 

 Vochting's little known Organbildimg im Pflanzenreich, published in 1878. 



One reason for the more rapid morphogenetic progress among zoologists 

 at first was the fact that they had easy access to the early embryonic stages 

 of their organisms whereas in seed plants the young embryo, buried inside 

 integuments and ovary wall, is difficult to study experimentally. In one re- 

 spect, however, the structure of these higher forms gives the investigator a 

 great advantage in developmental studies, for in their meristems they possess 

 permanently embryonic regions. A single plant thus provides readily accessible 

 and genetically uniform material in abundance where many stages in the 

 developmental process can be studied in one individual. This advantage is 

 now being actively exploited, especially by those who work with apical 

 meristematic regions. Here the steps in the development of lateral organs can 

 readily be traced. The occurrence of cell layering in these meristems has 

 been studied, and in some cases, particularly in periclinal chimeras, it is 

 possible to trace particular organs or tissues to specific layers. The subepi- 

 dermal layer in the shoot has been found to be the one from which sporo- 

 geneous tissue is derived and may thus be thought of as the germinal layer, a 

 sort of germ plasm. 



That layering in itself has little significance, however, is shown by the 

 fact that plants where the meristematic apex is irregularly cut up into cells, 

 as in many gymnosperms, develop in as regular a pattern as do layered ones. 

 Evidently the particular cellular configuration of an embryonic region — and 

 this is still clearer in determinate meristems — has little direct effect on the 



