ELEMENTARY STRVCTUEE. 



17 



in the lower Algse, as Protococcus {figs. 1 and 2) ; in pollen 



Fig. 28. 



{jig. 28) ; and in spores {fig. 6) ; more fre- 

 quently, however, the cells assume a more or less 

 elongated form and become oblong {fig. 32), or 

 cylindrical {fig. 29). In other cases again, we 

 fold that certain points of the cell-wall acquire a 

 special development, and become elevated from 

 its general surface as little papillae {fig. 28), j?tj/. 28. Spherical 

 warty projections {fig. 29), or cilioe {figs. 30, 31, poUen cell, 

 and 32), or are prolonged into tubular processes, or branched in 

 various ways. The hairs which are produced on the surface of 

 plants afford good illustrations of cells which are more or less 



Fig. 30. 



Fig. 29. Elongated cell covered witli warty projections. Figs. 30, 31, 



and 32. Ciliated cells. Fig. 33, Branched cell (Botrydium granulaUtm). 



unrestrained in their development {figs. 112-125) ; other instances 

 occur in the germination of most spores, and strikingly so in 

 those of many Algse, as Botrydium {fig. 33) ; also when the pollen 

 cells fall upon the stigma ; and numerous other illustrations will 

 be observed as we proceed with our subject. 



2. Size of the Cell. — The cells vary much in size in differ- 

 ent plants, and in different parts of the same plant. The par- 

 enchymatous cells, on an average, vary from about i^ to -—^ of 

 an inch in diameter ; others again are not more than ^^^ ; 'while 

 in some cases they are so large as to be visible to the naked eye, 

 being as much as ~ or even -'g of an inch in diameter. The 

 largestQCCi^ Jn the pith of plants,J n succulent p arts, an d jn -^frater 

 plants^ - ~' 



