4 INTRODUCTION. IV. 



ble kingdom. Notwithstanding whicli 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 afibrds 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 Algse 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 Avhich was seen to 

 spread over so vast an extent of ground by Captain Koss, 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 with 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, Avhen 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 tlie snow 

 fell, and its developement may have merely kept pace with the gradually deepen- 

 ing sheet of snow. That tliis 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 j^robably 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 Yolvox ; the chief difference between Protococcus 

 and Volvox being that the latter is clothed wdth 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 Algaa, and certainly (as we shall after- 

 wards see) their peculiar ciliary motion is no bar to this association. I do not 



