LECTURE XXIII. 



REPRODUCTION (continued). 



IN the present lecture we have to complete our account of 

 the facts of reproduction, and then to endeavour to arrive at a 

 comprehension of their physiological significance. 



The next series of facts to which we have to turn our 

 attention are those connected with development of the repro- 

 ductive cells. Beginning with the asexual reproductive cells 

 or spores, we have learned that they are produced by an 

 organ which we have spoken of generally as the sporangium. 

 In many cases there is no perceptible peculiarity in the sporan- 

 gium itself, or in the mode of development of the spores from 

 its protoplasm. In unicellular plants, like Yeast and Haema- 

 tococcus, the cell which constitutes the body of the plant, 

 constitutes the sporangium also ; and in a number of multi- 

 cellular plants, such as Ulothrix, Ulva, and Coleochaete, each 

 cell of the body may act as a sporangium and give rise to 

 spores. 



In some cases the spores are apparently formed from the 

 whole of the protoplasmic contents of the sporangium, so that 

 probably in the protoplasm of each spore all the various parts 

 of the protoplasm of the sporangium are represented. In many 

 cases, however, it has been ascertained that not all the pro- 

 toplasmic contents of the sporangium are used in the formation 

 of the spores. For instance, in many Fungi a considerable 

 portion of the protoplasm of the sporangium (or ascus) re- 

 mains over, as the epiplasm, after the formation of the spores ; 

 and in the development of the zoospores of the Algae (e.g. 



