CONFERVA MURALIS. 



C. filamentis fimplicibus tenuifiimis fafciatis rigidiufculis diffepimcntis 

 obfoletis ; articulis breviflimis. 



On moid Walls, Stones, Thatch, &c. 



IT can hardly fail to ftrike even the moft cafual obferver of plants, that the 

 green mattes obfervable on walls and ftones in damp fituations, mud owe their 

 origin to vegetable matter. Ulva crifpa is known often to occafion them, but ftill 

 more commonly do they proceed from the prefent plant ; the minutenefs of 

 which is fuch, that its having hitherto efcaped obfervation, is not wonderful, its 

 filaments being fo fine that the human eye can fcarcely diftinguifh them ; and 

 it is only by the afiiftance of the higheft powers of a compound microfcope that 

 we can form any juft idea of their nature. Its mode of growth is very denfely 

 matted, adhering clofely to the fubftance on which it grows, and infinuating itfelf 

 into every crevice : it is compofed of threads about an inch long, equal at each 

 extremity, varioufly twifted, and rather rigid; at lean: fo much fo, that when im- 

 merfed in water they do not follow the courfe of the current. Viewed with a 

 good glafs, the filaments are feen to be compofed of extremely fhort joints, in ge- 

 neral cylindrical, but fometimes affuming a globular appearance, interfered in an 

 irregular manner by fafcise : thefe I have obferved in fome others of this genus ; 

 they are feemingly of a diftincx nature from the diflepiments, being of a darker 

 colour and thicker fubftance ; but the moft remarkable difference confifts in 

 their having nothing of that curved appearance difcernible in the others, which 

 is occafioned by the cylindricity of the filaments. Some red ftrix, doubtlefs of 

 the fame nature, are reprefented in the figure of C. diftorta in the Flora Dan. 

 Tab. 920, to which this fpecies bears a considerable analogy; efpecially in the 

 remarkably abrupt manner in which fome of the joints appear altogether colour- 

 lefs, leaving thofe with which they are immediately conne&ed of their common 



