ALG.E. 435 



thalloid stem. From Anthoceroteae they differ in the absence of a 

 columella and of rudimentary elaters. They are interesting as exhibiting 

 the lowest type of organization in the Class to which they belong. They 

 are generally diffused, comprising 8 genera, with about 28 species. Genera : 

 Eiccia, Mich, ; Duricea, B. and Mont, j Sphcerocwyws, Mich. 



CLASS II. THALLOPHYTA. 



Definition. Cryptoganious plants producing in vegetation a 

 thallus, presenting no opposition of ascending and descending axis, 

 nor contrast of stem and leaf ; antherozoids never spiral ; repro- 

 duced by spores which are produced in parent cells, either forming 

 part of the vegetating thallus or growing upon the surface of defi- 

 nite regions of the thallus devoted to reproduction. Spores not 

 producing a prothallium, but reproducing the plant immediately. 



These plants correspond to the Thallogens of most authors ; their prin- 

 cipal points of distinction from Cormophytal Cryptogams are above given. 

 The vegetative structures of the plants of this group, which form their 

 principal bond of connexion one with another, and their most striking cha- 

 racter of distinction from the higher plants, present a great variety of 

 conditions within their own limits. The thallus is a purely cellular ex- 

 pansion, presenting no contrast of parts analogous to that between the 

 axis (stem) and the appendages (leaves and their modifications), which 

 exists in the higher plants ; hence they are necessarily devoid of true buds. 

 A special regularity, however, and a determinate direction of growth are 

 manifested more or less clearly in all cases, giving definite and character- 

 istic forms to the thallus. This is the case even when the thallus is reduced 

 to the condition of microscopic filaments, which elongate and spread in 

 determinate directions. The thallus is exclusively composed of cellular 

 tissue ; and its more minute differences in the various classes and families 

 of this division of the Vegetable Kingdom require microscopic inves- 

 tigation ; but certain broad distinctions may be laid down, sufficient for 

 the general discrimination of the classes in the more perfect forms. The 

 lower forms of the two classes of Thallophyta approach very closely in 

 their characters, on account of their great simplicity of organization, 

 which excludes the possibility of many differential characters. 



Division I. Algae. 



Gymnosporous Cryptogams living in water or in damp places 

 exposed to the light, extremely variable in size, form, colour, 

 and texture, free or attached by root-like organs, sometimes uni- 

 cellular, at other times having a branched pseudo-stem and leaf -like 

 appendages, sometimes of large size, but exclusively cellular in 

 structure and destitute of stomata. Plants multiplied by subdivi- 



2x2 



