84 THE QUANTITATIVE METHOD IN BIOLOGY 



The uniaxial system may produce more complicated systems 

 along two different lines : (i) by ramification ; (2) by cleavage 

 — i.e. 2l secondary segmentation in the direction of a new axis. 

 (See § yy.) 



§ 70.— RAMIFICATION OF THE UNIAXIAL SYSTEM. 

 FIRST EXAMPLE: PSEUDOCH^ETE.— Among the Alg(2 

 we find a number of simple examples of ramification of the 



uniaxial system. I take as 

 example Pseudochcete gracilis 

 (allied to Herposteiron), which 

 occurs as an epiphyte on aquatic 

 plants.^ A specimen x consists, 

 at first, of one row of cells united 

 into a uniaxial system similar to 

 Spirogyra. I represent this prim- 

 ary filament (pluricellular in- 

 dividual) and its axis by xA or 

 A. The individual (stem) A 

 creeping on the surface of an 

 aquatic plant, its axis may be 

 called horizontal. 



Certain cells of A produce a 

 lateral erect branch B (or xB), 

 the axis of which is vertical.^ 

 In each branch B a certain 

 number of segments (cells) are 

 produced by segmentation (cell- 

 division) : B becomes in this way 

 in its turn a uniaxial system. 

 According to the notation 

 adopted in § 54, each constituent segment (cell) of an individual 

 (stem) A is called A +1 {or xA +1) ; each ceU of an individual 

 B is called B + i (or xB + i). 



One might be tempted to believe that I am bringing useless 

 complications into the subject. I am, in fact, facing complica- 

 tions which really exist, and which must not be overlooked if 

 we want to apply the quantitative method. 



In Pseudochcete gracilis a fully developed specimen or indi- 

 vidual X is, indeed, a society constituted by one individual xA 

 (or A), and several individuals xB (or B), which consist them- 

 selves of simple individuals (cells) A +1 and B + i. All the 

 cells have been produced by successive divisions of one initial 



1 G. S. WEST, loc. cit., p. 88. 



2 Between a branch B and one of the reproductive branches (outgrowths) 

 of Spirogyra (§ 60) mechanical concordance very probably exists. It may be 

 recalled that mechanical concordance may be independent of any physiological 

 analogy smd of any morphological homology. 



Fig. 4. — Pseudochcete gracilis. (Sche- 

 matic, after WEST, loc. cit.. Fig. 30) 



