26 BRITISH CHAUOPHYTA. 



limited growth, and, with a few unimportant exceptions, 

 which will be referred to later, are produced in single 

 regular whorls, those belonging to each whorl being 

 approximately alike in size and structure. In their 

 earlier stages they are incurved, becoming more or less 

 spreading, but usually retaining an upward direction. 

 The number of normal branchlets in each whorl 

 ranges from five to twenty, but in the case of the 

 larger numbers some are evidently accessory. In 

 the Nitellese and in Nitellopsis the number is most 

 commonly six, in the rest of the Charede seven to ten. 



According to Sachs "the successive whorls of a 

 stem alternate, and in such a manner that the oldest 

 branchlets of the whorl, in the axils of which the 

 branches stand, are arranged in a spiral line winding 

 round the stem." Each branchlet originates from a 

 lateral node, formed from one of the peripheral cells 

 of the stem-node, and consists of a well-marked series 

 of nodes and internodes, but is unlike the stem in 

 having the growth limited (Fig. 5 BK., p. 24). As in the 

 case of the stem, the internodes consist of single cells 

 incapable of division, but increasing considerably in 

 length. Torsion is not usual, one side commonly main- 

 taining an inward position in relation to the axis of the 

 stem or branch, with the exception of the ultimate 

 rays in Nitella. In all the genera with the exception 

 of Nitelln, and usually to some extent in this also, 

 the structure of the branchlet is monopodial, that is 

 the axis is continuous in direction, the nodes and 

 internodes being produced in a direct line one above 

 another. There are, however, points of difference in 

 the several groups, which will be best dealt with 

 here. 



In GharayLamprothamniumyaud Lychnothamnus, each, 



