CLASSIFICATION OF THE PRIMORDIA 93 



periphery of the crown (sunshine) ought to be distinguished from 

 segments developed in the central parts of the crown (shade). 

 Adventitious branches proceeding from the main trunk or 

 from its base ought to be excluded (or to be investigated 

 separately). 



This subject is exceedingly complicated. Since the quan- 

 titative method is still incompletely established, it is advisable 

 to Hmit ourselves, for the quantitative specific description of 

 the properties of the vegetative parts, to the study of young trees 

 and shrubs raised from seed (p. 90). 



We may have recourse, however, to the quantitative in- 

 vestigation of the fertile parts ; for 

 instance, inflorescences, bracts, flowers, 

 fruits, seeds. These parts, indeed, are 

 brought into existence under certain 

 definite social conditions in each species 

 and are therefore comparable, at least 

 approximately. In these parts we find 

 a number of primordia large enough to 

 render possible, in a satisfactory way, 

 a quantitative description of aU the 

 species. 



1 2 



Fig. 6. — Prasiola parietina. 

 (Schematic, after WEST, 

 Fig- 36.) (i) young speci- 

 men (uniaxial system). (2) 

 Older specimen (rectangular 

 biaxial system ) 



§ 77.— RECTANGULAR BIAXIAL 

 SYSTEM, PRODUCED BY SECOND- 

 ARY SEGMENTATION OR CLEAV- 

 AGE OF THE UNIAXIAL SYSTEM 



(continued from § 69, p. 84). — An adult 

 specimen (individual x) of Spirogyra is 

 divided by segmentation into a number 

 of segments or individuals (cells) x+i, 

 which follow each other in the direction 

 of one axis. I call this axis the principal 

 or primary axis, or axis North-Soulh (NS). If each segment 

 (cell) is divided in its turn into two segments in the direction 

 of a secondary axis East-West (EW) perpendicular on NS, a 

 new system, represented in Fig. 6, 2, is obtained. This is a 

 rectangular biaxial system. I call segmentation or principal 

 segmentation (primary segmentation, segmentation NS) the division 

 in the direction of the primary axis NS and secondary segmenta- 

 tion or cleavage (segmentation EW) the division according to the 

 secondary axis EW. 



If the segmentation NS has been limited to the production 

 of two segments (cells), and if each of the latter has produced 

 only two segments by cleavage EW, a. system of four segments 



years begin to produce long shoots at a certain moment (for instance, in Sorbus 

 aucuparia). 



