ALG;E. 9 



Fungi (species of Lichen), to Sponges (e.g. Trentepohlia spongio- 

 phila, Struvea delicatula), and to sundry Infusoria and other 

 lower animals as Radiolarias, Hydra, etc. (the so-called Zoochlorella 

 and Zooxantella, which are perhaps partly stages in development 

 of various Green and Brown Alga>). 



Vegetative Organs. The cells in all the Alga? (excepting 

 certain reproductive cells) are surrounded by a membrane which 

 (with the exception of the Bacteria) consists of pure or altered 

 cellulose, sometimes forming a gelatinous covering, at other times 

 a harder one, with deposits of chalk or silica formed in it. The 

 cell-nucleus, which in the Schizophyta is less differentiated, may 

 be one or more (e.g. Hydrodicton, Siphonece) in each cell. Except- 

 ing in the majority of the Bacteria, colour materials (of which 

 chlorophyll, or modifications of it, always seems to be found) occur, 

 which either permeate the whole cytoplasm surrounding the cell- 

 nucleus, as in most of the coloured Schizophyta, or are con- 

 tained in certain specially formed small portions of protoplasm, 

 (chromatophores). 



The individual at a certain stage of development consists nearly 

 always of only one cell ; by its division multicellular individuals 

 may arise, or, if the daughter-cells separate immediately after the 

 division, as in many of the simplest forms, the individual will, 

 during the whole course of its existence, consist of only a single 

 cell (unicellular Alga?). In multicellular individuals the cells 

 may be more or less firmly connected, and all the cells of the 

 individual may be exactly alike, or a division of labour may take 

 place, so that certain cells undertake certain functions, and are 

 constructed accordingly ; this may also occur in parts of the cell 

 in the large unicellular and multinuclear Alga? (Siphonea?, p. 62). 



The cells in most of the Alga? belong to the parencliymatous form ; 

 these, however, in the course of their growth, may very often become 

 somewhat oblong; in many Alga? (particularly Fucoidea? and 

 Floridea>) occur, moreover, hyphce-like threads, which are very long, 

 often branched, and are either formed of a single cell, or, more 

 frequently, of a row of cells, having a well-pronounced apical 

 growth. The parenchymatous as well as the hyphae-like cells 

 may, in the higher Alga? (especially in certain Fucoidea? and 

 Floridea?), be further differentiated, so that they form well- 

 defined anatomico-physiological systems of tissue, i.e. assimilating, 

 conducting, storing, and mechanical. 



With regard to the external form, the thallus may present no 



