CYTOKINESIS AND THE CELL WALL 



181 



of the three reported by Fitting but points out that a portion of the 

 gelatinous layer may remain undifferentiated until a late stage and thus 

 appear like a third coat. 



In vascular plants the sporangium (the anther in angiosperms) is 

 lined by a layer of special nutritive cells known as the tapetum. In 

 many known cases, including Equisetum, Botrychium, Marsilia, and a 

 number of angiosperms, the boundaries of these cells break down, allowing 

 the protoplasts to coalesce and form a "tapetal Plasmodium," or "peri- 

 plasmodium." This flows in among the immature spores and contributes 

 to the development of their coats (Fig. 106). In Equisetum the spore 

 has three coats: an endospore, an exospore, and a perispore, the last being 

 formed by the Plasmodium and consisting of several layers. Upon the 



Fig. 105. Fig. 106. 



Fig. 105.— Developing megaspore coats of Selagindla rupestris. p, protoplast with nu- 

 cleus; en, endospore; s.m., undifferentiated portion of gelatinous layer; ex., exospore, of 

 which the denser portion is the "perinium." (After Lyon, 1905.) 



Fig. 106. — Exine of microspore (right) developing in contact with tapetal Plasmodium 

 (left) in Commelina. (After Tischler, 1915.) 



original membrane the Plasmodium deposits successively an inner 

 gelatinous layer, a second layer, an outer gelatinous layer, and finally a 

 layer which later splits up to form the characteristic appendages of the 

 spore. These four layers together constitute the perispore. While they 

 are in the process of formation the original spore membrane becomes 

 transformed into the exospore, and within it the endospore is developed 

 last of all." 



In the ascomycete Hydnotrya Tulasnei each spore, after its delimita- 

 tion from the cytoplasm of the ascus (p. 158), is surrounded by a thin 

 endospore. In the ascus cytoplasm near each spore there appears a 

 rounded mass of fluid, which enlarges, gradually surrounds the spore, and 

 develops into the elaborate exospore. In this case, therefore, the wall 

 material is visible before its deposition on the spore (Nemec, 1929d). 



The Cell Membranes of Animals. — The problem of the intimate 

 relation of protoplasm to partitions which subdivide it into cells is encoun- 



27 Beer (190%), Hannig (1911). 



