Its Structure tn Plants. 5 



of the same composition as starch but of different physical proper- 

 ties. In the embryonic stage of animals similar walled cells are 

 formed, though later on there is generally no wall round the proto- 

 plasts, and the tissues of a mature animal therefore have little 

 resemblance to those of a plant. To study the structure of proto- 

 plasm the individual cells have to be examined, and to do this 

 thoroughly requires the use of very high powers of the microscope. 

 Protoplasm is a colloidal form of matter, semi-fluid, but which will 

 not pass through a membrane, or only with great difficulty, and 

 hence it is supposed that its molecules must be comparatively very 

 large. When examined under slight magnification it appears 

 semi-transparent and jelly-like, and has generally a granular appear- 

 ance, but there is no trace of structure, save that in all or most cells 

 there is a denser portion or nucleus. Young cells of plants are 

 completely filled with protoplasm which doubtless consists almost 

 entirely of proteids. But in a very little time, as they grow larger, 

 cell-sap brought up from the root infiltrates through the walls, 

 and food matters are poured in from the leaves where they were 

 elaborated, and then clear spaces called vacuoles make their 

 appearance, which gradually coalesce till the whole internal space 

 seems one large vacuole and the protoplasm is pushed outwards 

 and forms a thin film round the walls. In these older cells, even 

 when slightly magnified, other bodies known as pltistids, usually of 

 a spherical or ellipsoidal shape, are seen floating in the protoplasm, 

 often in great numbers. They first appear around and near the 

 nucleus, are denser than the protoplasm in which they swim, and 

 in the interior cells of the plant and in roots are colourless, but in 

 the cells of the leaves are coloured green by a waxy substance 

 called chlorophyll, and in the petals of flowers are frequently red 

 or yellow. 



But when the protoplasm has first been carefully stained with 

 haematoxylon, a dye prepared from logwood, or with some other 

 staining matter, of which there are several, and the cells are sub- 

 mitted to examination under the highest powers of the microscope, 

 protoplasm assumes a completely different aspect, and a decided 

 structure, but one about which different opinions have been, and 

 still are, held, presents itself to view. The thinner, more fluid, 

 portion of the protoplasm (Cytoplasm) exhibits then the appearance 



