458 



THE AMERICAN NATURALIST. [VOL. XXXVIII. 



which contract and thicken as the plate develops. The bodies 

 composing the cell plate finally lie in a plane extending the 

 entire width of the spindle (Fig. 8 d) and they then broaden 

 and come in contact with one another to form a continuous 

 membrane, which, as has been said, may lie in a matrix of car- 

 bohydrate material. The cell plate grows rapidly as the central 

 spindle fibers shorten and contribute their substance to the 

 structure. During this contraction the surrounding cytoplasm 



FIG. 8. Segmentation of the Protoplasm, a, b, c, cleavage by constriction, d, cleavage by 

 cell plate, e, f, g, free Cell Formation. , cell division in Cladophora. b, cleavage of 

 spore plasm in Fuligo. c, spore formation in Hydrodictyon. d, first division of spore 

 mother-cell in Pellia. e, spore formation in ascus, i and 2 (Erysiphse) astral fibers cutting 

 out cytoplasm around nuclei, 3 portion of ascus with developing spores (Lachnea). f, 

 obgonium of Albugo, egg surrounded by membrane pierced by antheridial tube, ccenocen- 

 trum and female gamete nucleus within, g, egg of Ephedra with four embryo cells. After 

 Strasburger Harper and Timberiake. 



enters the region between the barrel shaped group of fibers and 

 the daughter nuclei (Fig. 8 d}. It is probable that the cell plate 

 is composed entirely of the substance of spindle fibers and in 

 consequence is kinoplasmic in character. The cell plate widens 

 with the accretion of material from the central spindle, which in 

 some cases is assisted by the radiating fibers that, lying outside 

 of the spindle, contract and add their material to the edge of the 

 plate. The cell plate thus extends laterally and finally reaches 



