4 Introduction 



itself. It is in these senses that the term morphogenesis will be used in 

 the present volume. 



Each of the major biological subsciences is intimately related to the 

 others. One cannot study genetics apart from physiology, for example, 

 or physiology from morphology, or taxonomy and evolution from all 

 these. It may well be maintained, however, that morphogenesis, since it is 

 concerned with the most distinctive aspect of life— organization— is the 

 crossroads where all the highways of biological exploration tend to con- 

 verge. Its subject matter deals with some of the most elusive and intract- 

 able phenomena in science, but it is here that the greatest discoveries of 

 the future are likely to be made. These will be significant not only 

 for biological problems but for many others that man faces. Even 

 philosophy, long concerned with problems of form, is still gaining 

 from this source fresh insights into its chief task, an understanding of 

 life. 



More study has been given to morphogenetic problems with animals 

 than with plants. A great advantage of animal material is that in many 

 groups the egg is discharged into water and the embryo develops there, 

 at least through its earlier stages, and is thus easily accessible for obser- 

 vation and experiment. Among higher plants, on the contrary, all the early 

 development of the embryo takes place within the ovule, surrounded by 

 many layers of tissue and relatively inaccessible. The result has been that, 

 save for rather special material like the egg of Fucus which can be 

 treated much like that of an animal, very little morphogenetic work has 

 been done on plant embryos. Modern techniques, however, by which 

 it is possible to grow the embryos of some higher plants to maturity in 

 culture, are making the science of experimental plant embryology a more 

 fruitful one. 



Workers with plants have a number of advantages, however. In plants, 

 permanently embryonic regions, the meristems, are available for study. 

 At the tip of shoot and root and in the cambial layers these are inde- 

 terminate and produce new plant structures almost indefinitely. Such 

 meristems are usually numerous or extensive on the same plant so that 

 ample material for the study of development, identical in genetic con- 

 stitution, is available. Growth and differentiation in the development of 

 a plant are thus continuing processes and not limited to a single and 

 often brief life cycle. 



Organs such as leaves, flowers, and fruits, which are determinate in 

 growth, pass through a cycle closely comparable to that of individual 

 animals, and morphogenetic problems can also often profitably be studied 

 in them. The fact that they are usually produced in abundance on a 

 single plant is a further advantage, for here the investigator need not be 

 concerned about genetic diversity in his material but can study strictly 



