SHULL: GENETICS 131 



tion brought about by meiosis, the "reduction division." The unfortunate con- 

 fusion of terminology in botanical and zoological literature in relation to sex 

 phenomena is still only partially resolved but there can be little doubt that a 

 common and concordant terminology will be ultimately achieved through the 

 influence of genetical considerations. The confusion began when botanists 

 took over the sex terms which had been long applied by zoologists and by 

 laymen,— by the botanists themselves, — in regard to diploid animals and 

 applied them to the haploid generation in plants which has no counterpart in 

 animals. 



To achieve complete harmony it is necessary only to limit the concept of 

 sex-homologies between plants and animals^ to the diploid generation of plants, 

 since it is the "sporophyte" of the higher plants that manifests Mendelian 

 phenomena in exact agreement with those exhibited by the bodies of animals. 

 The situation becomes clear if we take as the starting point for a comparison 

 of the life-cycle of plants and animals the moment of union between egg and 

 sperm. This brings the diploid resting-spore of the Chlorophyceae into a posi- 

 tion of homology with the body of an animal, and leads to recognition of the 

 fact that the fundamental difference between embryophytes and animals is 

 the fact that in the former, the ootids (megaspores) and the spermatids (mi- 

 crospores) develop parthenogenetically to form respectively the female and 

 male gametophyte generations, whereas in animals they are converted as a 

 rule directly into eggs and sperms. 



The closest relationship of genetics with the other biological disciplines is 

 that between genetics and cytology. Before the birth of genetics, cytology had 

 its major outlook directed toward comparative embryology. With the specific 

 recognition of the chromosomes as the determining mechanism of the Men- 

 delian phenomena, it has become obvious that cytology and genetics jointly 

 constitute the biology of the chromosome. Cytology represents the morphol- 

 ogical phase and genetics the physiological phase of the inheriting mechanism, 

 but the relationship is so close that it is frequently indicated by the use of the 

 term "cytogenetics" for this very fundamental scientific discipline. 



In all other branches of biological science, — taxonomical, morphological, 

 physiological, sociological, psychological, — the fact is of fundamental signi- 

 ficance that genes constitute the basic material with which the researches in 

 these several fields must deal. The origin and distribution of genes generally 

 follow a pattern of very great simplicity which must be taken into account in 

 laying out programs of experimentation, in analyzing the results of such ex- 

 periments, and in drawing tenable conclusions from them. Genetics, the 

 science of kinship, thus knits together, even to the most intimate details of 

 basic organization, the organisms with which every phase of biological science 

 deals, and strongly emphasizes the inherent kinship of all branches of biology. 



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