18 



EVOLUTION OF CELLULAR STRUCTURES. 



PARAGAMIC phase: 



KARY APSIS 



APAYLOGAMIC PHASE 



SYNAPSIS 



HAPUOGAMIC PHASE 



double nnm})er of cliromosomes. The binucleate structures of the 

 fung-i may })e referred to as the <q>t(ijl(Hiaiiiic j^hme. The so-called 

 "sexual generation" ma}- ))e called the haploganuc pltme in both 

 cases. These new terms might not be necessary if words were used 



for descriptive pur- 

 poses only, but in 

 the present instance 

 they have general 

 implications too im- 

 portant to be disre- 

 garded. 



H a p 1 o g a m i c 

 structures are built 

 between sy napsis" 

 and plasmapsis, 

 apaylogamic b e - 

 PLASMAPSIS tween plasmapsis 



Fig. 1.— Diagram showing tlie dilYerenl types of cell structures aud and karvapsis, par- 

 their position in the life history of organisms. a g a m i' C l>et WCCn 



karvapsis and sj^napsis. Between the three critical points of cyto- 

 logical activity there are three intervals, in which the organism can 

 pause to gain additional size or numbers Ijy vegetative division of 

 cells. The relations between the cell structures and the nuclear 

 processes are illustrated by the accompanying diagram (lig. 1). 



No organisms 

 have, however, 

 structures built in 

 all the three phases. 

 The relative impor- 

 tance of each phase 

 in the life histories 

 of the different 

 natural groups can 

 also be illustrated 

 by simple diagrams, 

 as shown in figure 2. 



The relative im- 

 portance of the dif- 

 ferent phases in the 

 life historv of the 



ljower groups 



Kt 7S 



HIGHER FUNGI 

 Kt 7S 



MOSSES 



-e- 



FERNS 



FLOWERING PLANTS 



Fig. 2.— Diagram showing the relative importance of the paragamio, 

 apaylogamic, and haplogamic phases in the life history of various 

 groups of organisms. 



various groups of organisms can be represented in another way, as 

 is shown on Plate I. The diagrams on thifi plate show in addition 

 a network of descent in its simplest form, composed of successive 

 generations linked together at the first stage of conjugation. The 

 generations themselves are seen to be composed of alternating 



