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M/NU TE STIiUCTURE. 



Crystalloids. 



S(mm1s, especially tlioso of an oily nature, as they approach 

 maturity and become dry, develope in their cells multi- 

 tudes of small rounded bodies of an albuminous nature 

 known as alKuronc-cjrains (Fig. 270), and these often 

 envelope minute substances of crj'stalline 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 cryntalloidH, 

 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. 2.')! shows a cell having two or three such crystal- 

 loids of a cubical shape. 



The aleurone-grains in seeds containing starch fill the spaces 

 between the starch-granules, as shown in Fig. 270, which 

 represents a cell from the cotyledon on the Pea. In oily 

 seeds, such as the Brazil-nut, they replace the starch. 



Other Cell-contents. 



Besides the important substances already enumerated as pro- 

 ducts of the protoplasm, 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, etc., chiefly in seeds), essential oils (turpentine, 

 oil of lemons, and essences of different kinds), gums, 

 resins, and various acids. 



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 enlarges and divides again, and so the 

 process goes on. When cell-division takes place in one 

 direction only, filaments or threads are formed ; if in 

 two directions, surfaces are formed; while division in 

 three directions gives rise to masses. Fig. 271 shows 

 dividing cells of the Bean in different stages. 



It is evident that every part of a plant, however much altered 

 in its later history, must in its earlier stages have con- 

 sisted of this thin-walled cellular sitbstance, or »ier^.y<e«^, 

 as it is called from its power of dividing. 



Cell-division, then, is the method of new cell formation which 

 prevails in the vegetative parts of the higher plants. In 



