558 MICEOSCOPIC FOEMS OF VEGETABLE LIFE THALLOPHYTES 



particles have little or no adhesion to each other ; or they may pre- 

 sent themselves (2) in the condition of an indefinite slimy film, or (3) 

 in that of a tolerably firm and definitely bounded membranous 

 1 frond.' The first of these states we have seen to be characteristic 

 of Palmoglcea and Protococcus ; the new cells which are originated 

 by the process of binary subdivision usually separating from each 

 other after a short time, and, even where they remain in cohesion, 

 not forming a * frond ' or membranous expansion. The ' red snow,' 

 which sometimes colours extensive tracts in Arctic or Alpine regions, 

 penetrating even to the depth of several feet, and vegetating actively 

 at a temperature which reduces most plants to a state of torpor, is 

 generally considered to be a species of Protococcus ; but as its cells 

 are connected by a tolerably firm gelatinous investment, it would 

 rather seem to be a Palmella. The second is the condition of Pal- 

 mella proper, of which one species, P. cruenta, usually known under 

 the name of ' gory dew/ is common on damp walls and in. shady 

 places, sometimes extending itself over a 

 considerable area as a tough gelatinous 

 mass, of the colour and general appearance 

 of coagulated blood. A characteristic 

 illustration of it is also afforded by the 

 Hcematococcus sanguineus (fig. 423), which 

 chiefly differs from Palmella in the partial 

 persistence of the walls of the parent-cells, 

 so that the whole mass is subdivided by 

 partitions, which enclose a larger or smaller 

 number of cells originating in the sub- 

 division of their contents. Besides in- 

 creasing in the ordinary mode of binary 

 multiplication, the Palmella cells seem 

 occasionally to rupture and diffuse their 

 granular contents through the gelatinous 

 stratum, and thus to give origin to a whole 

 cluster at once, as seen at e, after the 

 manner of other simple plants to be pre- 

 sently described, save that these minute 

 segments of the endochrome, having no 



power of spontaneous motion, cannot be ranked as zoospores. 

 The gelatinous masses of the Palmella are frequently found to con- 

 tain parasitic growths formed by the extension of other plants 

 through their substance; but numerous branched filaments some- 

 times present themselves, which, being traceable into absolute 

 continuity with the cells, must be considered as properly appertaining 

 to them. Sometimes these filaments radiate in various directions from 

 a single central cell, and must at first be considered as mere exten- 

 sions of this ; their extremities dilate, however, into new cells ; and, 

 when these are fully formed, the tubular connections close up, and the 

 cells become detached from each other. 1 Of the third condition we 



\This fact, first made public by Mr. Thwaites (Ann. of Nat. Hist. 2nd series, 

 vol. n. 1848, p. 318), is one of fundamental importance in the determination of the 

 real character of this group. 



FIG. 422. A, conjugating 

 microzoospores of Ulo- 

 thrix ; B, megazoospore 

 of Ulothrix, from Vines's 

 ' Physiology of Plants.' 



