INTRODUCTION TO CRYPTOGAMIC BOTANY. 



159 



Acetahularia, for the elliptic spores figured by Kiitzing, in the 

 threads which form the orbicular disc, have only been observed 

 in dried specimens, and we are ignorant of the nature of the 

 series of apertures on the surface of the internal circle of cells. 

 Suchcharacters are, however, not more incompatible with Gon- 

 fervacece than with Siphonece. In the more compound species, a 



Fig 41. 



a. Conferva clavata, var. Darwinii, Hook., from small specimens col- 

 lected by Mr. Darwin, nat. size. 



h. Acetabidaria mediterranean nat. size, from specimens communicated 

 by Nageli. 



c. Polyphysa penicillns, nat. size, from specimens sent from King 

 George's Sound, by Dr. Harvey, with a portion of the stem magnified. 



multitude of forms are produced, simulating Cacti, reticulated 

 corals, flabelliform corallines, &c., which are either beautiful 

 in themselves, or in their structure.* The genus Halimeda 

 (Fig. 42) has been well illustrated by Messrs. Derbfes and Solier, 

 and it is one of those productions which can be studied with 

 satisfaction only in their native locahty. The obovate lobes, 

 of which the plant is composed, are traversed by an immense 

 number of branched threads, which, through the whole of their 

 course, and throughout their ramifications, are without septa. 



* The best way of examining these, is by applying hydrochloric acid, 

 which changes the carbonate of lime into the soluble chloride of cal- 



