CYTOLOGY OF REPRODUCTION IN PLANTS 167 



pair of nuoloi. H(>rice this peculiar nuclear condition in a pnvi of the hfe 

 cycle, the possibility of determining the capacities of each sjjore of a 

 given quartet or octet, and the convenience and rapidity with which 

 the plants maj^ be cultured and subjected to biochemical analysis (page 

 202), have combined to bring these fungi from obscurity to a prominent 

 position in biological research. 



3. These chapters show in what a great variety of ways a given 

 process may be carried out or a given result attained. A recognition of 

 the unity underlying all this diversity should enable one to distinguish 

 more surely what is fundamental from what is accessory or only inci- 

 dental. Concepts based on only one or two typical cases often require 

 revision when viewed in the light of what occurs in organisms of many 

 kinds. Far too many definitions of biological phenomena are merely 

 descriptions of single examples of a class and fail to indicate what is 

 significant in all cases. The mastery of many definitions is a poor 

 substitute for the possession of a few broadly based concepts. 



Finally, an acquaintance with the cytological diversities of plants and 

 animals should contribute something to the value of one's speculations 

 on the origin of the cytological constitutions and reproductive processes 

 characterizing the various groups. This is a part of the great problem 

 of phylogeny, which, because of its complexity and the significance of 

 its conclusions, must be investigated with thoroughness and long suspen- 

 sion of judgment. In no other field of inquiry is it truer that ''it is 

 easy to use simple logic when the facts are few." 



