CELL-DEVELOPMENT. 



259 



Taking for our examination the more simple organisms 

 among vegetables, we shall find numbers which present, in 

 their earliest as well as in their permanent state, the cell 

 in its simplest condition, and its reproduction a bare re- 

 petition of the same thing. Unicellular plants, then, in 

 the strictest sense, are represented only by those in which 

 the whole cycle of life is completely shut up in the one 

 cell ; the first reconstruction or division being at once the 

 commencement of a new cycle, in which, consequently, 

 the whole vegetative life is run through in the same cell 

 where the prorogation also appears. 



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Fig. 144.— Cell Development. (Protococcus pluvialis.) 



Protococcus pluvialis, Kiitzing. Hcematococcus pluvialis, Flotow. ChlamidO' 

 encetM versatilis, A Braun. Chlamidococcws pluvialis. Flotow and Braun. 



a, division of a simple cell into two, each primordial vesicle having developed a 

 cellulin envelope around itself; b, Zoospores, after their escape from the 

 cells ; c, division of an encysted cell into segments ; d, division of another 

 cell, with vibratile filaments projecting from cell- wall ; e, an encysted cell ; 

 F, division of an encysted cell into four, with vibratile filaments projecting ; 

 o, division of a young cell into two. 



The most widely distributed of these single-cell plants 

 is the Palmoglcea macrococca, of Kiitzing, which spreads 

 itself as a green slime over damp stones, walls, &c. If a 

 small portion be scraped off and placed on a slip of glass, 

 and examined with a half or quarter-inch power, it will be 

 seen to consist of a number of ovoid cells, having a trans- 

 parent structureless envelope, nearly filled by a granular 

 matter of a greenish colour.  At certain periods this mass 

 divides into two parts, and ultimately the cell becomes two. 

 Sometimes the cells are united end to end, just as we see 



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