HANDBOOK OF SEA-WEEDS. 7 



the most rudimentary of all plants, and thus ot special interest 

 physiologically, as representing the component parts of which 

 higher plants are formed. They are subdivided into twelve 

 groups, as follows : 



The first group, Palmelleee, are unicellular plants, the cells of 

 which are either free or surrounded by a gelatinous mass, and 

 they are propagated by the division of the enclochrome. One 

 of the most remarkable of the species of this family is Protococcus 

 cruentus, which is found at the foot of walls having a northern 

 aspect, looking as if blood had been poured out on the ground 

 or on stones. Protococcus nivalis, again, is the cause of the red 

 snow, of which early arctic navigators used to give such marvel- 

 lous accounts. (Fig. 2.) 



The Desmideacese, together with the plants of the next succeed- 





Fig. 3. A, Fragment of a Filament of Zygnema, one of the Conjugates. 

 B, Closterium ; C, Euastrium ; two desmids. 



ing group, are favourite subjects of investigation or observation by 

 the possessors of microscopes, an attention they merit from the 

 beauty and variety of their forms. They are minute plants 

 of a green colour, consisting of cells generally independent 

 of each other, but sometimes forming brittle threads or minute 

 fronds, and are reproduced by spores generated by the conjuga- 

 tion of two distinct individuals. The process of conjugation in 

 Desmids and Diatoms consists in the union of the endochrome. 

 of two individuals, each of which in these families is composed 

 of a single cell. This ultimately forms a rounded body or rest- 

 ing spore, which afterwards germinates, the resulting plant not 

 however acquiring the normal form until the third generation. 

 (Fig. 3-) 



The Diatomaceje, closely allied to the preceding group in 

 structure and reproduction, are however distinguished from them 



