74 



INDIVIDUALITY IN ORGANISMS 



other parts of the plant body. In the complex higher 

 plant, stems, branches, buds, roots, and various other 

 parts possess a growing tip, at least during earlier stages, 

 and each such part is to a certain extent an individual. 



Figs. i8, 19. — Axial developmental gradients in embryonic stages 

 of plants: Fig. 18, embryo of moss, apical cell at upper end (from prepara- 

 tion loaned by W. J. G. Land); Fig. 19, proembryo of gymnosperm 

 {Ginkgo); apical region of plant arises from lower end (from Lyon). 



In most of the lower plants a single cell forms the apex 

 or center of the growing tip, and it may be larger than 

 other cells \Yith a gradient of decreasing size extending 

 from it, as in the stem of the alga in Fig. 20, but during 

 the course of plant evolution the apical cell gradually 



