PH^OPHYCE^E 105 



possess no definite growing point. The reproductive 

 organs are both unilocular and plurilocular sporangia 

 arising by the differentiation of a superficial cell or 

 of an outgrowth from one. The conjugation of 

 gametes has been observed in one form. 



The Thallus in the filamentous form is articulated, 

 and consists of several rows of cells, but sometimes 

 partially or even wholly of a single row. However, 

 most of the forms exhibit both a cortical tissue and 

 an internal one. The internal tissue consists of large 

 parenchymatous cells, and the cortical layer of smaller 

 assimilative cells, though these are commonly of 

 relatively greater size than in allied groups. Hairs 

 and paraphyses sometimes spring from the super- 

 ficial cells, the hairs with basal growth (at least in 

 the case of Punctaria, and more notably Hydrocla- 

 thrns) from pits resembling cryptostomata of simple 

 structure. The attachment of the thallus to the 

 substratum is either by means of a disc or by a weft 

 of rhizoids. Immediately above the attachment the 

 base of the thallus is commonly attenuated to a thin, 

 solid and short stalk. There is no true growing point, 

 and the growth is distributed more or less equally 

 over the whole thallus, but persists at the base, as a 

 rule, for a time after it has ceased elsewhere. The 

 development of the cryptostomata has been observed 

 in Hydrodathrus. In a surface view " an isolated cell 

 or several cells in a group become separated off from 

 the surrounding epidermis, each loses its polygonal 

 shape and becomes cylindrical. ... In a radial sec- 

 tion of such a group each cell is seen to be divided 

 by a transverse wall, but there is no indication of 



