50 MORPHOLOGY OF THE CELL. | 



most carefully examined consist of a mixture of two ingredients of different 

 solubility; the two are so combined that when the more soluble is slowly removed, 

 the less soluble remains as a skeleton (Nageli). 



Their form varies greatly in different plants ; they appear as cubes, tetf ahedra, 

 octohedra, rhombohedra, and in other forms ; usually, however, their crystallographic 

 characters cannot be exactly defined, a consequence of their small size and of the 

 inconstancy of their angles. 



In the rapidly growing organs of flowering plants they are known only in 

 LathrcEa squaviaria^ ; more commonly they are produced in cells where large 

 quantities of reserve-materials are collected which are only turned to use at a later 

 period. The crystalloids themselves appear to be a form of protoplasmic structure 

 especially adapted for a dormant condition (as in potato-tubers and many oily 

 seeds) ; they are seldom found in cells which contain sap (potato-tubers), but more 

 often in cells which do not contain it, and especially in oily seeds. Crystalloids 

 containing colouring matters are found in petals and fruits. Sometimes they are 

 formed only after the action of alcohol or a solution of sodium chloride on the 

 plants externally or internally (Rhodospermin). 



The crystalloids of potato-tubers are imbedded in the protoplasm; those that 

 are widely distributed in the tissues of Lalhrcea squamaria are contained in great 

 numbers in the interior of the nucleus; those found in oily seeds are generally 

 enclosed in aleurone-grains. 



The crystalloids discovered by Gohn in the tubers of the potato are convenient for 

 observation; they are found very abundantly in some kinds, in others less frequently, 

 in the parenchymatous cells which contain but little starch beneath the skin but 

 tolerably deep in this tissue, lying enclosed in the protoplasm. Generally they are in 

 the form of perfect cubes (less often of derivative forms, as tetrahedra). Those found 

 by Radlkofer in the nucleus of the cells of LathrcEa squamaria lie together in great 

 quantities ; they have the form of thin rectangular plates ; sometimes they have rhombic 

 or trapezoid forms ; Radlkofer thinks it most probable that they belong to the rhombic 

 system. In these cases they may be seen in sections without further preparation, and 

 their relation to their surroundings is clear. The case is different with the crystalloids 

 of oily seeds enclosed in aleurone-grains ; I shall recur to their properties, and will only 

 mention that from the brazil-nut they are obtained in quantities by washing the crushed 

 oily parenchyma by oil or ether, the crystalloids settling down in the form of a fine 

 powder; in sections but little can be made out. They were carefully investigated in 

 the isolated state by Nageli ; according to him they appear rhombohedral, octohedral, 

 or tabular; but it is uncertain whether they belong to the hexagonal or the klino- 

 rhombic system. Dried and then placed in water, they alter their angles about 2° or 3°; 

 in potash solution they swell strongly and alter their angles 15° or 16°. By weak acids 

 and dilute glycerin a substance is extracted, and a weak skeleton with firmer skin 

 remains behind. The crystalloids in the cells of the endosperm of Ricinus communis 

 are, like all crystalloids, insoluble in water, and are easily seen when thin sections of the 

 tissue are laid in water, which destroys the substance surrounding the crystalloid, and 

 sets it free. They frequently take the form of octohedra or tetrahedra, less often of 

 rhombohedra; but the system is not certainly determined. The crystalloids which 

 contain colouring matters were first detected by Nageli in an imperfect form in the 



^ [According to Prillieux, the brown colour of Neottia nidus-avis is due to brown crystalloids 

 which assume a green colour when the plant is immersed in alcohol or boiling water ; see Ann. des 

 Sci, Nat., 5th ser., vol. XIX. p. 108.] 



