386 PRACTICAL BOTANY 



tissues, either after dissolving the lime with acetic acid, or, 

 better, by grinding as in the preparation of geological sections : 

 in the latter case observe 



1. The successive pear-shaped joints of lime-incrusted tissue : 

 these can be recognized externally with the naked eye. 



2, The intervening transparent zones of tissue with pliant 

 mucilaginous walls. 



The whole is made up of cells of nearly equal size, arranged 

 in linear series, which correspond to one another in such a way 

 that the cells appear in fan-like zones. Here again there is no 

 single central series larger than the rest. 



E. Observations may also be made with advantage on speci- 

 mens of Lemanea, a genus of dark olive-green, fresh- water Algse, 

 included in the Floridese : these plants grow attached to rocks in 

 mountain streams. Note especially 



1. The simple filamentous, and branched proembryos similar 

 in many respects to that of Chara : these are known as the 

 " Chanlransia " filaments, and it is by means of them that the 

 plant is attached to the rocks. 



2. The more complex " reproductive thallus " which is pro- 

 duced as a lateral branch upon it : in the character of the apex, 

 and in its mature structure, it is not unlike that of some species 

 of Polysiphonia : it has clearly marked nodes, around which the 

 irregular antheridial patches are situated. 



Transverse and longitudinal sections should be cut, from which 

 it will be seen that the " reproducth e thallus " consists of a 

 central series of elongated cells, which traverses a cavity filled 

 with mucilage, and is connected by lateral struts, at points be- 

 tween the nodes, with the cortical tissue : the latter consists of 

 relatively large internal cells, and relatively small superficial ones. 



VII. Having distinguished with a lens, or under a 

 low power, a specimen bearing tetraspores, mount a 

 portion of it as before directed (taking care that young 

 branches as well as mature ones are represented), and 

 examine under a medium or high power. Note 



1. That the regularity of the tissues of the thallus is 



