64 CHARACEJ:. 



gametangia conjugate with one another; the product of the conju- 

 gation swarms about for some time, rounds off, and then surrounds 

 itself with a cell-wall. The zygote germinates after a period of 

 rest and then produces a sexual plant. The aplanospores (game- 

 tangia) thus represent the sexual generation. 



Class 7. Characese. 



The thallus has a stem with nodes and internodes ; and whorls 

 of leaves, on which may be developed the antheridia and oogonia, 

 are borne at the nodes. Vegetative reproduction by bulbils and 

 accessory shoots. Zoospores are wanting. The antheridia are 

 spherical, and contain a number of filaments in which the spirally 

 coiled spermatozoids, each with two cilia, are formed. The oogonium 

 is situated terminally, and is at first naked, but becomes later 

 on surrounded by an investment, and forms after fertilisation the 

 so-called " fruit." The oospore, after a period of rest, germinates 

 by producing a " proembryo," from which the young sexual plant 

 uri.ses as a lateral branch. The Characeaa are distinguished by the 

 structure of their vegetative system as well as by the spirally- 

 coiled spermatozoids, and stand as an isolated group among the 

 Thallophytes, of which, however, the Siphonete appear to be their 

 nearest relations. They were formerly, but wrongly, placed near 

 the Mosses. The class contains only one order, the Characese. 



Order 1. Characeae. Alga? with a peculiar odour, often 

 incrusted with lime, and of a brittle nature. They generally grow 

 gregariously in large masses at the bottom of fresh and brackish 

 water, and are from a few inches to more than a foot in height. 

 The stem has long internodes which in Nitella are formed of one 

 cylindrical cell; in Chara of a similar cell, but closely surrounded 

 by a cortical layer of smaller ones. The protoplasm in contact 

 with the cell- wall exhibits in a well-marked degree the movement 

 of rotation (cyclosis), carrying the chlorophyll corpuscles along 

 with it. The internodes are separated from each other by a layer 

 of small cells (nodal cells) from which the leaves are produced. 

 The leaves are borne in whorls of from 5-12 which regularly 

 alternate with one another as in the higher verticillate plants ; a 

 branch is borne in the axil of the first formed leaf of each whorl 

 (Fig. Gl A, ). 



The leaves are constructed in the same manner as the stem ; 

 they are divided into a series of joints, but have only a limited 



