THE VEGETABLE CELL. 



41 



ters (usually red or blue) are dissolved in it ; and still more 

 rarely is the quantity of the xincoloured substances, such as gum, 



dissolved in it, so 



great 



as to increase in a striking manner its 



power of refracting light. 



In many, yet comparatively rare, cases, the cell-sap of particular 

 cells becomes wholly displaced by compounds -which the cell itself 

 prepares, e. g., etherial oils. 



Ohser'o. Among the organs of the higher plants, ripe seeds alone bear 

 to be perfectly dried without being killed ; the older wood of trees may 

 also lose a great quantity of its sap without death ; the limit to which this 

 is possible is as yet unknown. The rest of the organs, particularly the 

 leaves, do not bear any considei^able loss of water. It is diiforent in many 

 lower plants, especially the Mosses, Lichens, and many Algse, e, g., m 

 Nostoc^ which may be completely dried up without injury. 



c. Granular structures. 



In the majority of parenchymatous cells, organic structures — 

 usually of granular form — are met with, at all events at certain 

 periods of the life, swimming in the cell-sap or slightly adherent 

 to the walls. Two of these, the chlorophyll granules and starch 

 are very generally diffused. 



(JkloTopliyll (leaf-green), on the presence of which ^'^9- ^5. 



depends the green colour of plants, never occurs 

 dissolved in the sap, but always in the form of a 

 softish mass of definite or indefinite shape ; many 

 phytotomists have asserted the existence of a green- 

 coloured cell-sap, but I have never been able to 

 nncl iu4 



Amorphous clilorophyll forming patches or tlnreads 

 which adheres to the cell-wall and the granules con- 

 tained in the cell, is of comparatively rare occur- 

 rence, yet it occurs here and there in the Phane- 

 rogamia, in the same cells with the chlorophyll 

 granules. Usually chlorophyll possesses a sharply 

 defined form. In certain Algse it presents itself in 

 the form of flat bands, in Conferva zonata, Dra- 

 parnaldia plumosa, &a, in each cell as a trans- 

 verse annular band ; in Zygnema (fig. 45), in the 

 form of a spirally wound band ; in Mougeotia, in 

 the form of a flat or curved plate lying in the in- 

 terior of the cell, &a In the gi^eat majority of 

 plants, however (see fig. 10), it possesses the form 

 of globules, which sometimes lie upon the wall of zm^ema. 

 the cell (where they are usually irregularly scat- 

 tered, but in Chora arranged in rows), sometimes swim in the 

 cell-sap, and sometimes surround the nucleus. 



But a very small portion both of the band-shaped masses in 



