4 
INTRODUCTION. 
IV. 
ble kingdom. Notwithstanding which lowly position in the scale of being, they 
display an infinite variety of the most exquisite forms and finely sculptured 
surfaces ; so that their study affords as much scope for the powers of observation as 
does that of the creation which is patent to our ordinary senses. These tribes are 
however omitted from this essay, because they have been made the objects of special 
enquiry by Professor Bailey of West Point, whose memoir in the second volume 
of the Smithsonian Contributions is referred to for further information. 
But Desmidiacece and Diatomacece are not the only Algae of this simple structure. 
The lowest forms of the order Palmellacece , such as the Protococcus or Red snow 
plant, have an equally simple organization. The blood-red colour of Alpine or 
Arctic snow which has been so often observed by voyagers, and which was seen to 
spread over so vast an extent of ground by Captain Ross, in his first arctic journey, 
is due to more than one species of microscopic plant, and to some minute infusorial 
animals which perhaps acquire the red colour from feeding on the Protococcus 
among which they are found. The best known and most abundant plant of this 
snow vegetation is the Protococcus nivalis , which is a spherical cell, containing a 
carmine-red globe of granulated, semi-fluid substance, surrounded by a hyaline 
limbus or thick cell-wall. At maturity the contained red matter separates into 
several spherical portions, each of which becomes clothed witli a membranous 
coat ; and thus forming as many small cells. The walls of the parent whose whole 
living substance has thus been appropriated to the offspring, now burst asunder, 
and the progeny escape. These rapidly increase in size until each acquires the 
dimensions of the parent, when the contained matter is again separated into new 
spheres ; giving rise to new cells, to undergo in their turn the same changes. And 
as, under favourable circumstances, but a few hours are required for this simple 
growth and developement, the production of the red snow plant is often very 
rapid : hence the accounts frequently given of the sudden appearance of a red 
colour in the snow, over a wide space, which appearance is ascribed by common 
report to the falling of bloody rain or snow. In many such cases it is probable 
that the Protococcus may have existed on the portion of soil over which the snow 
fell, and its developement may have merely kept pace with the gradually deepen- 
ing sheet of snow. That this plant is not confined to the surface of snow is well 
known ; and Captain Ross mentions that in many places where he had an opportu- 
nity of examining it, he found that it extended several feet in depth. It has been 
found both in Sweden and Scotland on rocks, in places remote from snow deposits ; 
and it probably lies dormant, or slowly vegetates in such cases, waiting for a supply 
of snow in which it grows with greater rapidity. 
The structure and developement which I have described as characterizing 
Protococcus , are strikingly similar to those of what are commonly considered 
minute infusorial animals, called Volvox ; the chief difference between Protococcus 
and Volvox being that the latter is clothed with vibratile hairs, by the rapid 
motion of which the little spheres are driven in varying directions through the 
water. Many naturalists, and some of high note, are now of opinion that Volvox 
and its kindred should be classed with the Alga?., and certainly (as we shall after- 
wards see) their peculiar ciliary motion is no bar to this association. I do not 
