188 



The following paper on a new plant, having been previously 

 offered by the author, is here inserted in a more full and de- 

 tailed form : 



Hydrothjria venosa ; a new genus and sjjccies of the Colle- 

 macege. Read before the Essex Institute, June 8, 1853, by 

 John Lewis Russell, Prof, Bot. Mass, Hort. Soc, &c. &c. 



The Collemacese compose a tribe of plants connected with 

 the lichenes, yet having very distinct characters. Their com- 

 mon type may be represented by Nostoc, but superior to that 

 alga by the presence of external apothecia. In collema the 

 thallus is a gelatinous mass, which is permeated by moniliform 

 and hyaline threads, and the two faces of which, or the upper 

 and lower epidermal portions of the thallus cannot be readily 

 distinguished from the rest. In leptogium we rise towards the 

 lichens, and we shall accordingly find in its epidermis a cellu- 

 lar tissue formed of polyhedral cells, notwithstanding the cen- 

 tral and deeper parts of the thallus do not differ from those of 

 collema. 



There are many species of these two genera, which are com- 

 mon in this vicinity. They grow on the bark of trees, upon 

 rocks, and even upon the earth ; subject and fitted to the varied 

 changes of atmospheric conditions, in the same way as are many 

 other of the lower cryptogams. 



The subject of this communication seems to me to hold an 

 intermediate rank between these two, I have called it Hydro- 

 thyria or Watershield, in allusion to its aquatic habits, and 

 from its bearing distinct shield-like apothecia like the colle. 

 mata. Another most striking peculiarity is to be perceived 

 in the strongly veined under surface ; these veins traversing 

 that part of the thallus in a flabelliform manner, reminding us 

 of the Peltigera among the lichens. 



On the sixteenth of July 1851, after herborizing in com- 



