218 THE ALG^E 



generally some shade of green. The sexual organs and cystocarps 

 are enough like those of Nemalion to make it as good a form to 

 illustrate the sexual processes and life history of the red algae 

 as the latter type, and it is sometimes more available for inland 

 classes. Batraclwspermum grows in clear brooks and is generally 

 found in its best condition in late winter and early spring. 



245. Polysiphonia. Polysiphonia illustrates some further 

 complexities in the life history of the red algre which are not 

 present in Nemalion and Batrachospermum. The filaments of 

 these beautiful plants consist of rows of cells, called siphons, 

 connected with one another in an elaborate manner. There is 

 a central siphon, around which are arranged a circle of outer 

 siphons variable in number for different species. 



The sexual organs are found on. separate plants. The male 

 organs, antheridia, are modified branches (Fig. 204, A) that de- 

 velop an outer covering of small cells which form the sperms 

 (Fig. 204, B). The female organ is found on a small branch 

 (Fig. 204,6') and consists of a carpogonium, with its trichogyne, 

 accompanied by a number of vegetative cells which later take 

 part in the development of the cystocarp. The fusion of a sperm 

 with the trichogyne fertilizes the carpogonium as in Nemalion. 

 There are two sets of activities concerned with the development 

 of the cystocarp: (1) there are some remarkable cell unions 

 between the fertilized carpogonium and neighboring cells (aux- 

 iliary cells) for nutritive purposes, and then the development of 

 carpospores from the large fusion cell which is formed ; (2) ac- 

 companying this activity there is the development of an urn- 

 shaped envelope (Fig. 204, D), from some of the vegetative cells 

 around the carpogonium, and this is clearly a protective structure 

 to contain the carpospores. The first set of activities corresponds 

 to the development of the simple cystocarp of Nemalion. The 

 second set forms the additional urn-shaped protective case. The 

 cystocarp of Polysiphonia is therefore a system of two tissues, 

 one derived from the fertilized carpogonium, and the other from 

 the vegetative cells of the parent plant. 



