PALMELLACEiE. 1 1 7 



development is very rapid, we may easily account for the rapidity with which the 

 Protococcus nivalis has been seen to extend, and also for the vast surface covered by so 

 minute an organism. Each individual is not more than tdtht of an inch in diameter, yet 

 the surface of snow visibly reddened by the congregated masses often covers hundreds 

 of square miles. A species very similar, if really different, called P. pluvialis, is found 

 in shallow pools of rain water, on the surface of rocks, in gutters of houses, &c, ; and 

 has been noticed in very distant parts of the globe under various climatial conditions ; 

 and of this species a most elaborate monograph,* illustrated by figures, has been given 

 by De Flotow, in the Nov. A ct. Leop. Carol. Nat. Cur. vol. 20, where no less than 

 twenty-two distinct and many more subdistinct varieties, or rather states, are enume- 

 rated, described, and measured to fourteen places of decimals (!) and figured. Several of 

 these forms are endowed with movements resembling those of the infusorial animalcules, 

 and have been described as animalcules by Shuttleworth in his account of the Red Snow 

 (Bib. Univ. Geneva, Feb. 1840.J 



A little higher in organisation than Protococcus is the genus Gloeocapsa (Hwmato- 

 coccus) in which what is only a passing phase of the Protococcus becomes a permanent 

 character. In this we have several cells (of the structure of Protococcus) enclosed 

 within a common, primary cell, which is persistent, or at least partially so. In some 

 species (as in G. Hooker i) the primary cell-coat exfoliates repeatedly, the old coats 

 remaining permanently attached on one side to each other, and to the cell, which per- 

 petually bursts through them ; and thus a sort of spurious frond, simple or branching, 

 is formed, consisting of exuvias, each branch being tipped with the living cell, which 

 shines like a gem at its summit. These plants occur generally in damp situations, on 

 rocks and among mosses, aboiit the spray of cascades, &c., and Kiitzing has described 

 and figured upwards of fifty. 



Next come the Palmdlce proper, where a large number of protococcoid cells are enclosed 

 within a common gelatine, in which they sometimes appear to be distributed without 

 order ; and sometimes arranged in a subquaternary manner. In this latter case the 

 structure approaches very closely to that of Tetraspora, a genus we have already 

 referred to the Ulvacece ; but which is placed by many authors next to Palmella. 

 Possibly among these obscure jilants forms are associated in one genus which will be 

 separated when their development is better understood. Among some of the Palmellce 

 Broome and Thwaites have described and figured a more definite organization than was 

 previously known ; namely, that the apparently scattered cells of the mass are connected 

 in an early stage of growth, by means of slender gelatinous threads, with a central cell 



* This extraordinary essay is well wortli looking at — (I will not say carefully pemsing) — as one of the most 

 remarkable commentaries on the text, " how gi'eat a flame a little fire kindleth." The object to be examined 

 is a microscopic Alga of the simplest possible structure, being in fact merely an isolated living ceU. All that 

 need to be said of its history might, one would suppose, easily have been wi-itten in a page or two. But the 

 learned and most laborious author has occupied nearly two hundred large quarto pages on this theme ; and 

 not content therewith, has appended long tables of decimal measurements of microscopic ai-eas and volumes, 

 whose only reference to his subject appears to be that they enable him to arrive at such important calculations 

 and useful results as describing the mean difl"erences of the shorter and longer diameters of different individuals 

 of his Protococcus, and their mean comparative bulk and spherical aben-ation. In computing these tables, the 

 decimals have been carried sometimes to fourteen places, and in most cases at least to si.x. 



