Butters: observations on rhodvmenia. 209 



from .5 mm. to 2 cm. in width. The smallest are almost circu- 

 lar in outline. Those somewhat larger (up to about 5 mm. in 

 diameter) are usually somewhat oval, being elongated in the 

 direction of the long axis of the frond. The larger perforations 

 are of irregular elongated outline. Sometimes these perfora- 

 tions are exceedingly numerous, as many as four or five per 

 square cm. being not uncommon. 



In some specimens numerous proliferations are borne on the 

 faces and edges of the lamina and also on the stipe. These are 

 cylindrical bodies, about i mm. in diameter, seldom more than 

 25 mm. long, often flattened somewhat towards the apex and 

 often branched once or twice or deeply lobed at the apex. 



In two specimens the upper portions of the laminae present a 

 peculiar mottled appearance which was at first supposed to be 

 due to the presence of tetraspores. It appears that this is not 

 the cause of the phenomenon noted. This subject will be dis- 

 cussed further under the description of the cystocarp. 



The entire stipe was present in only one of the specimens at 

 hand. In this it was 3.5 cm. long, about i mm. in greatest 

 diameter, flattened somewhat, parallel to the flat surface of the 

 lamina, passing insensibly into the lamina above, and expand- 

 ing abruptly below to form the holdfast, which is a small, thin, 

 irregular disk, about 5 mm. in diameter. 



All of the specimens have cystocarps scattered irregularly 

 over the entire surface of both sides of the lamina. These are 

 bodies 1-1.5 mm. in diameter, nearly hemispherical, or pro- 

 truding slightly at the apex, and are extremely numerous, as 

 many as fifteen being often found on one square cm. of the 

 lamina. 



Minute anatomy : Lamina. — The lamina consists of pseudo- 

 parenchymatous tissue of which two principal areas may be dis- 

 tinguished in the cross-section (a), a central layer of large- 

 celled; and (b) a cortical layer of small-celled tissue (Fig. 2). 



{a) The cells of the central area are large, generally some- 

 what flattened parallel to the surface of the frond, isodiametrical 

 in tangential section (Fig. 3). The cells vary greath' in size, 

 the average being 73.5 x 105 mic, while cells occur as small as 

 6 X 14 mic, and as large as 100 x 200 mic. The largest cells 

 are situated near the central portion of this area, and from them 

 the size of the cells decreases quite regularly towards the more 

 superficial portions. The more superficial cells of this area 



