246 MOTILE CONDITION OF PROTOPHYTES. 



tions. One of the most remarkable of these varieties is the motile 

 condition, which seems to be common, in some stage or other of 

 their existence, to a very large proportion of the lower forms of 

 Aquatic Vegetation ; and which usually depends upon the extension 

 of the Primordial Utricle into one or two thread-like filaments, 

 endowed with the power of executing rhythmical contractions, 

 whereby the cell is impelled through the water. 



188. As an illustration of this peculiar mode of activity, which 

 was formerly supposed to betoken Animal life, a sketch will be 

 given of the history of a plant, the Protococcus pluvialis (Plate 

 vm. Fig. 2), which is not uncommon in collections of Rain-water,* 

 and which, in its motile condition, has been very commonly regarded 

 as an Animalcule, its different states having been described 

 under several different names. In the first place, the colour of 

 these cells varies considerably ; since, although they are usually 

 green at the period of their most active life, they are sometimes 



* The Author had under his own observation, more than twenty years 

 ago, an extraordinary abundance of what he now feels satisfied must 

 have been this Protophyte, in a rain-water cistern which had been 

 newly cleaned-out. His notice was attracted to it, by seeing the surface 

 of the water covered with a green froth, whenever the sun shone upon it. 

 On examining a portion of this froth under the Microscope, he found 

 that the water was crowded with green cells in active motion ; and 

 although the only bodies at all resembling them of which he could find 

 any description, were the so-called Animalcules constituting the genus 

 Chlamydomonas of Prof. Ehrenberg, and very little was known at that 

 time of the ' motile ' conditions of Plants of this description, yet of the 

 Vegetable nature of these bodies he could not entertain the smallest 

 doubt. They appeared in freshly collected rain-water, and could not, 

 therefore, be deriving their support from Organic matter; under the 

 influence of light they were obviously decomposing' Carbonic Acid and 

 liberating Oxygen, and this influence he found to be essential to the con- 

 tinuance of their growth and development, which took place entirely 

 upon the Vegetative plan. Not many days after the Protophyte first 

 appeared in the water, a few Wheel- Animalcules presented themselves ; 

 these fed greedily upon it, and increased so rapidly (the weather being 

 very warm) that they speedily became almost as crowded as the cells of 

 the Protococcus had been ; and it was probably due in part to their 

 voracity that the plant soon became less abundant, and before long dis- 

 appeared altogether. Had the Author been then aware of its assumption 

 of the ' still ' condition, he might have found it at the bottom of the 

 cistern, after it had ceased to present itself at the surface. — The account 

 of this Plant given above, is derived from that of Dr. Cohn, in the 

 " Nova Acta Acad. Nat. Curios." (Bonn, 1850), Tom. xxii. ; of which an 

 abstract by Mr. George Busk is contained in the "Botanical and Physio- 

 logical Memoirs," published by the Ray Society for 1853. This excellent 

 observer states that he kept his plants for observation in little glass 

 vessels, having the form of a truncated cone, about two inches deep, and 

 one inch and a quarter in diameter, with a flat bottom polished on both 

 sides, and filled with water to the depth of from two to three lines. " It 

 was only in vessels of this kind," he says, "that he was able to follow 

 the development of a number of various cells throughout its whole 

 course." Probably he would have found the Tube-Cells represented in 



Fig. 106, if he had been acquainted with them, to answer his purpose 

 just as well as these specially constructed vessels. 



