FOEMATION OP NEW CELLS. 167 



- these - often envelope minute substances of crystalline 

 aspect, which, however, under the action of potash and 

 other re-agents, undergo such changes of form as to -lead 

 to the belief that they are not true crystals. They are 

 called crystalloids, and are to be regarded as forms of 

 protoplasm. 



Occasionally crystalloids are observed without the 

 albuminous envelope, as, for example, in the tuber of the 

 Potato. Fig. 214 shows a cell having two or three such 

 crystalloids of a cubical shape. 



The aleurone-grains in seeds containing starch- fill the 

 spaces between the starch-granules. In oily seeds, such 

 as the Brazil-nut, they replace the starch. 



281. Other cell-contents. Besides the important 

 substances already enumerated as products of the proto- 

 plasm, many others are found, such as sugar, inuline (a 

 substance nearly related to starch, and found in a few 

 special plants), fixed oils (castor, olive, linseed, &c., chiefly 

 in seeds), essential oils (turpentine, oil of lemons, and 

 essences of different kinds), gums, resins, and various 

 acids. 



282. How new cells are formed. There are 



several methods by which new cells are produced, but in 

 the higher plants the common method is that of cell- 

 division. . We have already stated that only the newer 

 thin-walled cells are capable of exercising this function. 

 The process is briefly as follows : in the cell about to 

 divide, the protoplasm first separates into two portions, 

 each containing part of the nucleus ; then a partition-wall 

 of cellulose is developed between the two portions, thus 

 forming two cells out of the original one, Each part then 



