THALLOPH YTA—ALQM 



51 



■'■a 



lopment of the structure varies very greatty in different groups, 

 leading in all ultimately to the production of a fruit-like structure 

 which is known as a cystocarp, and which is really the sporophyte 

 phase of the plant. It consists essentially of a cluster of car- 

 Xwsporangia, variously arranged and often enclosed in a definite 

 encasement of filaments or cells. There are five different types 

 of formation. The first is seen in the Nemalionace.e ; here 

 from the fertilised carpogonium filaments known a,s goni7noblasts 

 grow out, often in dense clusters. The terminal cells of the 

 filaments are the carposporangia, and each produces internally 

 a single carpospore. The whole group constitutes the cystocarp 

 {fig. 800), which is consequently not enclosed in any specially 

 differentiated case. Some- 

 times the gonimoblasts arise ^^' 

 from the upper part of the 

 carpogonium, sometimes 

 from its side. In some of the 

 families the cystocarp is im- 

 mersed in the tissue of the 

 thallus. In the Gelideae the 

 ceils of the gonimoblast be- 

 come united here and there 

 to certam cells of the thallus, 

 from which it absorbs nou- 

 rishment. 



The second type is fur- 

 nished by the Gigartinace^ ; 

 in this, besides the branches 

 which carry the carpogonia, 

 other special cells are pro- 

 duced on the thallus near 

 them, generally in pairs. These cells are known as auxiliary 

 cells. When the carpogonium has been fertilised it does not give 

 rise at once to gonimoblasts, but puts out a short protuberance 

 known as an oohlastema filament. This makes its way to an 

 auxiliary cell, and the contents of the two fuse. The gonimo- 

 blasts arise from the resulting cell and branch in the interior 

 of the thallus, the cystocarp being thus embedded in its sub- 

 stance. The fruit tlius arises from the auxiliary cell rather than 

 immediately from the carpogonium as in the Nemalionacese. 



The thnd type, characteristic of the Khodomeniace^, is still 

 more complex. The formation of the cystocarp is indirect as in 

 the last case, the carpogonium conjugating with an auxiliary cell. 



k2 



Nemalion. 



Fig. 800. 1. Cystocarp 

 a. Carpospores. 



2. Cystocarp of Lejolisia. 

 spores, c. Wall of cystocarp. d. Carpo- 

 spore escaping. After Ku}'. 



h. Carpo- 



