OF THE ELE3IEXTAEY STfirCTUEES. 



73a 



protoplasmic contents in each of these then secretes a layer of 

 membrane on its outside, and thus four perfect cells are formed 

 in the cavity of their parent. As these continue to enlarge, the 

 walls of the parent cells, and subsequently those of the spe- 

 cial parent cells, become ruptured or dissolved, and the cells 

 being thus set free, the process is completed. (See page 252, 

 Rnd Jig. 546.) The manner in which spores are formed in the 

 higher Flowerless Plants is substantially the same in most cases. 

 It sometimes happens, however, that in the development of pollen 

 and spores, the special parent cells are not formed, as has been 

 shown by Schacht in the pollen of (Enothera, and in the spores 

 of Anthoceros IcBvis ; and by Henfrey in the spores of Marchantia 

 polymorpha {fig. 1104). 



Fig. 1104. 

 a b 



Fig. 1105. 



c d 



Fifi. 1104. a. Cylindrical cell from which are formed the parent cells of 

 the spores of Marchantia polymorpha. p. Primordial utricle of the 

 parent cells, b. The same cell converted into a string of cells, c. One 

 of the parent cells Isolated, with four primordial utricles of the spores. 



(/. The four spores free. After Henfrey. Pig. 1105. Formation of 



zoospores in Achlya proUfm-a. After Carpenter. 



In other cases, instead of the development of only four second- 

 ary cells in the cavity of the parent, we have a large number 

 formed {fig. 1105, a), which either escape {fig. 1105, b) from it 

 clothed by a cellulose coat, as is ordinarily the case, or this is 

 secreted after their separation from the parent cell, as in the 

 zoospores of the lower Algae. Some of these modifications of the 

 process of cell-division are closely analogous to the ordinary 

 process of free cell-formation, to which they are referred by 

 Henfrey and other histologists. 



