THE SMITHSONIAN INSTITUTION. 91 



of examining it, lie found that it extended several feet in depth. It 

 lias been luiind both in Sweden and Scotland on rocks, in places re- 

 mote from snow deposites ; and it probably lies dormant, or slowly 

 vegetates in such cases, waiting for a supply of snow, in which it grows 

 with greater ra})idity. 



The structure and development which I have described as charac- 

 terizing ProtococcHs, are strikingly similar to those of what are com- 

 monly considered minute infusorial animals, called Vol vox ; tlie chief 

 difference between Proiococcus and Volvox being that the latter is 

 clothed with vibratile hairs, by the rapid motion of which the little 

 spheres are driven in varyiug directions through the water. Many 

 naturalists, and some of high note, are now of o])inion that Volvox and 

 its kindred should be classed with the Algie, and certainly (as we shall 

 afterwards see) their peculiar ciliary motion is no bar to this associa- 

 tion. I do not pronounce on this question, because it does not im- 

 mediately concern our present subject, and because, in all its collat- 

 eral bearings, it requires more attentive examination than it has yet 

 undergone. 



In Frotococcus the cell of which the plant consists is spherical or 

 oval ; in other equally elementary Algaj the cell is cylindrical, and 

 sometimes lengthened considerably into a thread-like body. Such is 

 the formation of Oscillaforice. In Vaucherice there is a further advance, 

 the filiform cell becoming branched without any interruption to its 

 cavity ; and such branching cells frequently attain some inches in 

 length, and a diameter of half a line, constituting some of the largest 

 cells known among plants. 



In all these cases each cell is a separate individual : such plants 

 are therefore the simplest expression of the vegetable idea. But even 

 in this extremest simplicity we find the first indication of the struc- 

 ture which is to be afterwards evolved. Thus in the spherical cell we 

 have the earliest type of the cellular system of a compound plant 

 developing equally in all directions; and in the cylindrical cell, the 

 illustration of the vertical system developing longitudinally. These 

 tendencies, here scarcely manifest, become at once obvious when the 

 framework begins to be composed of more cells than one. 



Thus in the genera nearest allied to Frotococcus, the frond is a 

 roundish mass of cells cohering irregularly by their sides. From 

 these through Falmtlla and Tetraspora we arrive at Viva, where a 

 more or less compact membranous expansion is formed by the lateral 

 cohesion of a multitude of noundish (or, by mutual pressure, polygonal) 

 cells originating in the quadri-partition of older cells ; that is, by the 

 original ceils dividing longitudinally as well as transversely, thus 

 forming four new cells from the matter of the old cell, and causing 

 the cell-growth to proceed nearly equally in both directions. Start- 

 ing, therefore, from Frotococcus, and tracing the development through 

 various stages, we arrive in JJlva at the earliest type of an expanded 

 leaf. 



In like manner the earliest type of a stem may be found by tracing 

 the Alga3 which originate in cylindrical cells. Here the new cells 

 are formed in a longitudinal direction only, by the bipartition of the 

 old cells. Thus, in Conferva^ where the body consists of a number 



