Chcetophoracece 83 



met with in the Ulotrichaceae ; in fact, many authors place this 

 genus in the Ulotrichaceae. 



Species of this genus are rarely met with in the British Isles. C. involuta 

 Reinsch (which includes C. nuda Reinsch), the cells of which are 23 30 p, in 

 diameter, is known from Ireland (fig. 26 A C) ; C. conferta West (fig. 26 E 

 and F) is known from the English Lake District, and C. geminella Wolle var. 

 minor Hansg. has been observed from Yorkshire and Cambridgeshire. 



Family 5. CHJETOPHORACEJE. 



This family of the Chsetophorales has undoubtedly arisen by a 

 further specialization of the Ulotrichaceae. The thallus is branched 

 and the branches are attenuated, sometimes being produced into 

 long multicellular hairs. As a rule the thallus is differentiated 

 into a recumbent or creeping portion, attached to a substratum by 

 rhizoids, and an erect, branched portion. The creeping portion 

 presents a more or less moniliform or torulose appearance, is 

 branched, arid the cells are very similar to those of the Pleurococ- 

 caceae. The cells of the erect portion of the thallus are elongated, 

 more or less swollen, but not torulose, and the branching is most 

 irregular, the terminal cells of the branches frequently forming 

 long hyaline hairs. 



There is a single chloroplast in each cell, consisting of a 

 parietal, more or less irregular plate, containing one or more 

 pyrenoids. In the attenuated cells towards the ends of the branches 

 the chloroplast becomes reduced, and in the long, hyaline, terminal 

 cells it is entirely absent. 



Zoogonidia may be produced from all the cells of the thallus 

 except those forming the rhizoids or the terminal hairs of the 

 branches. The number which may arise from a single cell varies 

 from 1 to 16, depending upon the age of the plant, the size of the 

 cell, and other indeterminable causes. Both macrozoogonidia and 

 microzoogonidia are produced, exhibiting a considerable range in 

 size, and they possess either two or four cilia and a pigment spot. 

 They rapidly come to rest, lose their cilia, and germinate directly. 



On the direct germination of a zoogonidium the cilia are lost, a 

 cell-wall arises, and increase in length takes place, one pole being 

 greatly elongated to form a hyaline, rhizoid-like projection. Septa 

 soon appear dividing the original long cell into several shorter 

 ones, and if the adult plant be a strongly branched one, the 



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