173 



THIRD SUBDIVISION AND CLASS IX. 



CHARACEyE. 



The true position of this small group in a natural system of classifi- 

 cation has been a subject of much controversy. By some writers of 

 high authority it is regarded as occupying the highest place among 

 green Algge. On the other hand, although without any lignification of 

 their tissue, the Charace^e display, in the structure of their vegetative 

 organs, a distinctly higher type of structure than the Thallophytes, in the 

 distinct differentiation of the plant into a primary axis or stem, and 

 secondary axes or branches ; but the branches are similar in structure 

 to the primary stem. They are, in fact, Cormophytes rather than 

 Thallophytes ; and it seems best to retain them as a distinct subdivision 

 intermediate between the Muscinese and the highest Algge. 



The plant is acrogenous, growing by means of an apical cell contained 

 in an apical bud ; the main stem has indefinite apical growth, the branches 

 increasing by definite apical growth. The branches and the organs of 

 sexual reproduction grow in the axils of other lateral organs of more 

 simple structure, which are usually termed leaves ; those that subtend 

 the reproductive organs being by some writers described as bracts or 

 bracteoles. In all the Characeae these appendicular organs spring in 

 whorls from well-defined nodes of the primary stem, imparting the pecu- 

 liar habit to the plants by which they are distinguished from nearly 

 all other Cryptogams. Each internode consists, in the Nitelleae, of a 

 single very large cell extending along its whole length, and many times 

 longer than broad. In the majority of the Chareae this internodal cell 

 is invested by a layer of similar elongated cells of much snialler diameter 

 arranged spirally round it, collectively known as the cortex, and giving 

 the stem the appearance of being spirally striated. Each node consists, 

 in the corticated species, of a single layer or plate of small cells from 

 which the cortex is derived. From the nodes spring the whorls of 

 branches and their subtending leaves. The branches are altogether 

 similar in structure to the primary axis. The leaves have also, in the 

 Chareae, a simple cortical layer, with the exception of the apex, where 



