FKESH- WATER ALG^. 97 



generally fixed to a substratum, manifests a marked contrast 

 between base and apex. 



Sphceropha is the simplest of the Oospores. The filaments 

 consist of very long cells, the contents of which are a colourless 

 protoplasm, a green chlorophyll, a watery liquid and granules of 

 starch, the whole so disposed that the liquid element forms large 

 vacuoles in a row, like the pearls of a necklet engirdling the 

 plant. 



On approaching fructification the vacuoles multiply to such an 

 extent as to give the endochrome the appearance of a frothy mass, 

 in which the starch granules are irregularly scattered. Soon 

 after the starch granules assemble in twos, threes, or larger num- 

 bers, and around these groups the green plasma becomes more 

 plentiful, so that in time they appear as so many equadistant cysts 

 in the axis of the thread. These green clots assume a stellate 

 appearance, then become flattened to resemble partitions, which 

 by and by disappear, and the whole thread breaks up into a 

 number of free globular masses, which, after various modifications, 

 become the young spores. 



All the cellules of the same filament do not undergo the 

 modifications described. In a large number the green rings^ 

 interspersed with colourless vacuoles, gradually change to a reddish 

 yellow, and the grains of starch disappear. Soon the coloured 

 matter thus formed becomes granular, and is finally broken up 

 into numerous rod-like corpuscles. 



In the sexual reproductive process some cells give rise to 

 antherozoids, others to oospheres ; after fecundation the oospore 

 changes from green to red, and becomes enclosed in a stellate 

 covering. The filaments of Sphceropha do not root themselves, 

 both extremities being similar, and vegetation being carried on by 

 sub-division of the central cells, so that the terminal cells remain 

 the oldest. 



Vaiicheria consists of a single elongated cell, branched in 

 various ways and usually fixed to one spot. 



The antheridia are lateral, sessile, or cut off by a septum from 

 the branch bearing them ; the genus has been sub-divided, accord- 

 ing to the special characters of the antheridia. The oogonia are 

 lateral, sessile, or stalked, and after fertiUsation become red or 



