8 



ORGANOGRAPHY. 



pollen (/^rs. 11 and 12); 

 Figs. 11 and 12. 



i>' 



>>^ 



in the spores of many of the lower Alga;, 

 as Protucoccus (fig. 148), &c. More 

 frequently, however, the cells assume 

 a more or less elongated form (fig. 

 13) and become oblong or cyUndrical. 

 In other cases again, we find that 

 certain points of the cell-wall acquire 

 a spherical development, and become 

 elevated from its general surface as 

 little papillre (y?/;. 13), or cilia; (figs. 14, 15, and 16), or are 

 ])rolonged into tubular processes, or branched in various ways. 

 The hairs produced on the surface of plants will afford us good 

 illustrations of such cells (figs. 96 — 99); other instances occur in 



Fig. 15. Fig. 14. 



Figs. 11 and 12. Spherical 

 pollen cells. 



Fig. 13. 



Fig. 16. 



Fig. 13. Elongated cell covered with warty projections Figs. 14, 15, and 



IG. Ciliated cells Fig. 17. Branched cell iBotrydium granulatum). 



the germination of most spores, and strikingly so in those of many 

 Algre, as Botrydium (fig. 17); also when the pollen cells fall 

 upon the surface of the stigma ; and numerous other illustra- 

 tions will be observed as we proceed with our subject. 



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

 ferent pLants, and in different parts of tlic same plant. The par- 

 enchymatous cells, on an average, vary from about ^^^ to ^^ 

 of an incli in diameter ; others again are not more tlian ^^^ ; 

 while in some cases they arc so large as to be visible to the 

 naked eye, being as much as -^^ or even jf^ of an inch in 

 diameter. The hirgcst occur in the pith of plants, in succulent 

 parts, and in water ]>lants. 



The dimensions of proscncliymatous cells generally afford a 

 great contrast to those of tlie })arcnchymatous, for wliile we find 

 that their transverse diameter is commonly much less, they become 



