10 DEVELOPMENT OF CELLS. 



by minute rectangular crystals adhering to each other. Unger detected 

 oxalate of limp crystals in Ficus bengalensis and Calathea zebrina. 



19. Chlorophyll*- (^Xagoj, green, and <p^Xo(/, a leaf), or the green 

 colouring matter of plants, floats in the fluid of cells, accompanied by 

 starch grains. It has a granular form (fig. 39 w, 42 c), is soluble in alcohol, 

 appears to be analogous to wax in its composition, and is developed 

 under the agency of light. Its granules are usually separate, but some- 

 times they unite in masses (fig. 37 c). Other kinds of colouring matter 

 are also produced during vegetation, and occur in the form of fluids or 

 of granules in the interior of cells. 



20. Oils and Resinous matter are found in the interior of cells, as 

 well as in intercellular spaces. The cavities containing them are deno- 

 minated cysts, reservoirs of oil, and receptacles of secretions. They are 

 easily detected in the rind of the orange and lemon, in the myrtle tribe, 

 and in Hypericum. When small portions of the fresh leaf of Schinus 

 mollis are thrown on water, the resinous matter, by its rapid escape, 

 causes them to move by jerks, and the surface of the fluid is covered 

 with the exudation. In the bark of the Fir tribe there are cavities 

 with thick walls containing turpentine. In the fruit of UmbelliferEe, 

 canals occur called vittce \vitta, a head-band, from surrounding the 

 fruit), containing oil. 



21. Air ceils, or cavities containing air, consist either of circum- 



scribed spaces surrounded by cells (fig. 43), or of lacunae 

 formed by the rupture or disappearance of the septa be- 

 tween a number of contiguous cells, as in grasses, Equise- 

 turn, Umbelliferous plants, and pith of Walnut. They 

 are often large in aquatic plants, and serve the purpose of 

 43 floating them, as in Pontederia, Trapa, Aldrovanda, and 

 sea-weeds. 



3. DEVELOPMENT AND FUNCTIONS OF CELLS. 



22. The subject of Cell-development, or Cytogenesis (XVTOS, a cell, and 

 yfviai;. origin), which has given rise to great diversity of opinion among 

 physiologists, is still involved in much obscurity. By some it is 

 affirmed that the first appearance of vegetable tissue is in the form of 

 a mucilaginous fluid, which, gradually thickening, becomes hollowed 

 into a number of small cavities constituting the future cells. Schleiden 

 believes that the cell is formed from the nucleus, to which he gave 

 the name of Cytoblast (XJ/TO?, a cell, and /sxewroV, a germ), or cell-germ, 

 from its supposed generative function. This cytoblast, according 

 to him, is the part first formed. It acts by attracting the mucilagi- 

 nous matter in which it lies, and forming around itself a sort of gela- 

 tinous covering. There is thus produced round the nucleus a closed 



Fig. 43. Air-cells in Ranunculus aquatilis. 



