CLASSIFICATION OF THE PRIMORDIA 



87 



n 



In many plants we find hairs consisting of one row of cells, 

 which are similar to an erect branch of Ps. gracilis, the terminal 

 cell being different from the others in one or 

 another way. In such a hair the same 

 primordia as in an individual B of Ps. 

 gracilis are found. The mechanical concord- 

 ance between both objects is obvious. (Compare 

 Fig. 5 with the erect branches in Fig. 4.) 



§ 72.— RAMIFICATION OF THE UNI- 

 AXIAL SYSTEM. FIRST EXAMPLE: 

 PSEUDOCH^TE GRACILIS {continued). 

 CLASSIFICATION OF THE PRIMORDIA.— 

 The primordia of Pseudochcete gracilis ^ may be 

 classified according to the following scheme 

 (compare §§ 57, 60) :— 



(i) Stem and branches (axes) : two sorts [A 

 and 5). 



(2) Nimiber of each sort. 



(3) Relative position of the axes A and B. 

 This is a phyUotaxic property. 



(4) Nimiber of axes of segmentation in stem 

 and branches (one axis in A and in B). 



(5) Number of segments (cells) in A and B. 



(6) Form of the segments (ceUs) in A and B 

 (cone, truncated cone, etc.) . 



(7) Dimensions of the segments (cells) in A 

 and B. 



(8) Total length of the stem A and the 

 branches B. 



(9) Gradation (branches B) : «., with refer- 

 ence to the breadth (conical form) ; /?, with 

 reference to the variation of the length of the 

 successive cells. (In the creeping stems A 

 gradation is, I think, imperceptible.) 



(10) Degree of gradation in the branches 

 B (compound property) . 



Since several branches B occur, we may 

 content ourselves with measuring the properties 

 5, 6, 7, 8, 9 and 10 only in the longest branch. 

 Witi regard to 7 (dimensions of the cells in 

 the branches B) we may Umit ourselves to the 

 basal and the terminal cell of the longest erect 

 branch. 



The above scheme is appUcable to any object 

 similar to Ps. gracilis in its structural plan. 

 1 The contents of the cells being excluded. 



A 



Fig. 5. — A hair con- 

 sisting of four 

 cells. (Petiole of 

 Erodium moscha- 

 tum) 



Most of the 



