EXPERIMENTAL MORPHOLOGY 151 



sumption is made that the union of two \'ariegating allelo- 

 morphs does not form a successful zygote, and this converts 



the typical ratio iDD rzDR :i RR ' to 2l)R:iRR. This 

 would mean that all the variegated plants are heterozygotes. 

 To test this assumption a number of crosses w'ere made be- 

 tween \ariegated and green individuals and in all such 

 cases the offspring were \ariegated and green in the ratio 

 1:1 as the hypothesis would require. 



It appears that Pchirgu)iiiim zoualt' presents a somewhat 

 similar situation, though this has not yet been sufficiently 

 demonstrated. In this case the DD group is not wholly 

 absent but Is represented by completely white individuals 

 which must succumb at an early stage of development owing 

 to their inability to manufacture sufficient carbo-hydrate 

 food. 



THE EXPKRIMENTAL MORPHOLOGY 

 OF PLAN! S. 



The region where plant physiology and plant morphol- 

 ogy overlap is considered by the comparatively new branch 

 of botanical science called experimental morphology. It is 

 the aim of this subdi\'isi()n of botany to understand, on the 

 one hand, what are the controlling forces involved in the 

 development of the different plant structures, and, on the 

 other, within what limits it is possible for these structures 

 to vary. One aspect of the problem is physiological, lying 

 in the broader proxince of irritability, and the other is mor- 

 phological, lying in the province of variability. Ihe two 

 sides of the series of questions here involved must, of course, 

 be de\eloped hand in hand. 



The main results so far obtained in this fascinating field 

 of study hax-e just been brought together by Prof. Goebel, 

 of Munich, in an "Introduction to the experimental morph- 

 ology of plants."' The publication of this work, which is 

 as elementary as is compatible with the nature of the subject. 



