134: R. CRAITHWAITE ON THE HISTOLOGY OF PLANTS. 



chymatous tissue, and in general in all young cells in a state of 

 active growth, in which the parietal current is not observable. 

 The internal circulation commences at the time when the proto- 

 plasm and cell-sap separate, and vacuolation commences in the 

 former, and although probably existing in the youngest condition 

 of the cell, it is only when the granules become developed that we 

 can distinguish it. The jointed staminal hairs of Tradescantia are 

 well adapted to observe the gradual formation of the internal cur- 

 rent ; by selecting young flower bads of various ages we may find 

 hair-cells in every stage of progress, and a con*esponding develop- 

 ment of protojjlasm, but a warm sunny day is requisite to exhibit 

 the movements to advantage. The cause of these movements 

 appears to depend on vital chemical action, and is without doubt 

 intimately connected with the process of nutrition. The chemical 

 reactions of protoplasm are the same as those of the primary cell 

 membrane, showing that it belongs to the albuminous class of bodies ; 

 the outer homogeneous layer, is, however, less deeply coloured. 



The Cell Sap is a watery fluid, containing various organic and 

 inorganic compounds in solution, such as sugar, gum, dextrine, 

 tannin, colouring matters, &c. 



Formed Organic Contents of Cells. 



Having thus glanced at the anatomy of the plant cell in its 

 active living state, we may refer briefly to a few other matters 

 found in cells, resulting from vegetative action, and there stored 

 up for future use in the economy of the plant or as effete material. 

 The chief of these are Starch, Inulin, Chloroj^hyl, Aleuron, Crystals 

 and certain colouring matter. 



Starch is most widely diffused through the whole vegetable 

 kingdom, and is of vast importance from the part it plays in the 

 food supply of the whole world. 



Starch occurs almost entirely in parenchymatous cells, and in 

 many tissues at all times of the year, while in others it is found 

 only during the period of rest, being dissolved and consumed in 

 the process of renewed growth, e.g., in the potato, which we plant 

 in spring a heavy solid tuber, and turn up again in autumn a light, 

 empty skin. 



In size the starch granules vary considerably, both in different 

 plants and according to their age in the same plant, the limits 

 being about '001 and -2 mm. in diameter. Their form is also 



