NOSTOC. 279 



able to distinguish them when they become the subject of pen 

 or tongue ; we therefore treat them briefly and retain such names 

 as are most familiar. The collector should bear in mind that 

 Nostocs are liable to great variations both in size and color ; some 

 may be microscopical in size to-day ; at a later season they will 

 be as large as peas or cherries ; some may have thin colorless 

 membranes, while others have firm teguments of yellow or brown 

 color ; the trichomes of some may be very slender and almost 

 colorless, others are thicker, light yellow, brown, or lighter or 

 darker aeruginous, apparently so distinct and unlike one another 

 they have been accounted different species, but in reality the 

 changes merely indicate a variety of stages of development or 

 decay. 



In a comparatively recent work (Italian) a number of Nostocs 

 are described and illustrated as N. macrosporum, Menegh. ; N. 

 rupestre. Kg.; N. coriaceum, Yauch. ; N. verrucosum, Vauch. ; N. 

 tenuissimum, Kab. ; all of which forms occur together, here, in 

 mass on dripping rocks, and evidently constitute but one species ; 

 then there are some noted as having the filaments sheathed, 

 others as unsheathed ; neither are such properly separated, be- 

 cause in the younger stage of growth the sheath is not devel- 

 oped; in older forms (and yet not always) the sheath becomes 

 evident. 



Various stages of growth of another JVosfoc-form, found at 

 different seasons of the year, and by different individuals, have 

 given rise to a number of names for the same plant. In early 

 Spring it is found as a soft, floating, gelatinous stratum, and is 

 called N. comminutum, Kg. ; or N. piscinale, Kg. ; when the filaments 

 are not surrounded by a soft gelatin, then they form N. tenuissi- 

 mum, Kg. These moniliform threads soon separate and sink. Next 

 they are found as very small thalli attached to submerged grasses 

 or mosses producing the form of N. minutissimum. Kg., or N. de- 

 pressum. Wood. These thalli grow, and when about the size of 

 peas, pass for N. coeruleum. Lyngb. Later in the season, about 

 September, all of those which were so numerously attached to 

 the plants a month or two earlier, will have disappeared, but 

 instead there will be found on the bottom of the pond, larger 

 thalli, from the size of cherries to that of plums ; this is N. 

 prnniforme, ' Both ) Ag., and is one of our most attractive Nostocs 

 with its firm, smooth, glossy periderm and its dark aeruginous 

 green color. Having attained this mature condition, they soon 

 fade ; the cytioplasm becomes watery, the periderm breaks and 

 dissolves and the contents are scattered. 



