POLYSIPHONIA 389 



2. Cystocarps of ovate form : these consist of closely 

 aggregated, small-celled tissue : they occupy the same 

 position as the lateral branches in a vegetative 

 thallus. 



3. Compare numerous specimens, and note cystocarps 

 in various stages of development. 



By careful observation on material taken in early summer the 

 various steps in the development may be traced, such as the 

 origin of the cystocarp as a multicellular body, seated at a point 

 immediately below the apex of a short lateral branch of the 

 thallus, and recognized as a darker group of cells : the mode of 

 segmentation of the young cystocarp, and the formation of the 

 trichogyne as an elongated thread-like cell, which overtops the 

 apex of the branch on which it is borne : its fertilization by a 

 spermatium, and the further growth of the cystocarp. 



As examples of simpler structure of the fruit may be suggested 

 Batrachospermum, and Polyides or Dudresnaya, the latter genera 

 being specially remarkable for the indirect character of the process 

 of fertilization. 



The case of Lemanea is worthy of note : the carpogonia are 

 formed internally, but with a projecting trichogyne : in spring 

 (March) these may be seen projecting from the surface of the 

 thallus, and are perhaps as easily recognized as in any of the 

 Floridese. In summer the carpospores are to be found borne' on 

 branching filaments which occupy the large mucilage cavities in 

 the thallus. Transverse sections of the thallus should be made 

 so as to demonstrate the internal position, structure, and mode of 

 development of the fruit, in material taken in early summer. 



In the forms with more complicated structure, the cystocarp is 

 often embedded in the tissue of the thallus : sections should be 

 cut to illustrate this in Chondrus crispus. 



X. Embed mature cystocarps of P. fastigiata in 

 paraffin, and cut from them median longitudinal sections : 

 mount in glycerine, and observe 



1. The short thick stalk of the cystocarp. 



