Sinnott • Morphology as a Dynamic Science 



89 



of course, questions the great impor- 

 tance of the experimental method or 

 the desirabihty of resolving as promptly 

 as possible the problems of develop- 

 ment into the simpler ones of physics 

 and chemistry-; but as a matter of sober 

 fact, most of these problems are not yet 

 in a position where they can profitably 

 be attacked in this manner at all. Be- 

 fore we can intelligently set up experi- 

 ments to determine the integrating and 

 coordinating growth processes which 

 control development and produce spe- 

 cific forms, we must first obtain precise 

 descriptive information as to exactly 

 how development proceeds. Further- 

 more, in most cases where as the result 

 of experiment a difference of form or 

 structure has been produced, it is of 

 the utmost importance to analyze in 

 morphological terms the exact changes 

 involved. Long before normal develop- 

 ment, or experimentally produced 

 changes in it, can be expressed in phys- 

 ical or chemical terms, they must be 

 expressed in morphological terms. The 

 first step backward from the visibile end 

 result of a developmental process to- 

 ward the ultimate inducing cause — be 

 this gene, hormone or radiation— must 

 be a more refined description of this 

 result and of the visible steps which 

 lead up to it. This is obviously a job for 

 the morphologist. 



But it is not only a descriptive 

 knowledge of development as expressed 

 in words that the student of mor- 

 phogenesis requires. In one important 

 particular the morphologist must 

 change his usual technique if he is to 

 make it serve the dynamic aspect of 

 his science: He must present his results 

 in quantitative terms. Only thus can 

 they yield themselves to precise analy- 

 sis and to interpretation in terms of 

 the physical sciences, and only thus can 

 they serve as a means for the discover^' 

 of new facts and relationships. To the 

 scalpel and forceps, the microtome and 



the microscope, the morphologist must 

 add the ruler and the scale as part of 

 his equipment if he is to make his data 

 serviceable to morphogcnetic science. 



In my own laboratory we have been 

 studying the genetic basis of shape dif- 

 ferences in the fruits of the Cucurbi- 

 taceae. These characters can be de- 

 scribed by the patterns and shape in- 

 dices of the mature fruits, but such tell 

 only part of the story. It is essential to 

 learn the developmental history of each 

 type if we are to find what the genes 

 actually control here. When length 

 and width are measured at successive 

 stages from ovary primordium to ripe 

 fruit it is found that they grow at dif- 

 ferent rates, so that the fruit changes 

 in shape somewhat during its develop- 

 ment. The relative growth rate is con- 

 sistently different in different races. 

 In the Hercules Club, length grows 

 faster than width, so that the fruit be- 

 comes progressively more elongate. In 

 the bottle gourd, on the other hand, 

 width grows faster than length. Within 

 a given race, however, this relationship 

 is so unvar}ang that it may be expressed 

 by a simple value or constant and thus 

 used to describe ver\' precisely the most 

 important aspect of a fruit-shape dif- 

 ference. This constant relative growth 

 rate segregates in inheritance and 

 seems to be what the genes governing 

 shape primarily control. It thus con- 

 stitutes an important step into that un- 

 known territory between the gene and 

 the visible shape which this determines. 



Such examples could be multiplied 

 almost indefinitely, and from work 

 with animals as well as with plants. 

 The whole domain of developmental 

 morpholog}', illuminated by the ideas 

 and viewpoint of morphogcnetic re- 

 search and attacked by quantitative as 

 well as qualitative methods thus offers 

 a wide field for fruitful investigation. 



For the welfare of biology as a 

 whole, therefore, it is my plea that 



