10 CONTENTS OF CELLS. 



threads, or embedded in the substance of the membrane. The addi- 

 tion of acetic acid often renders the nucleus distinct. 



Starchy matter is found in cells, which constitute the tissue 

 called by Morren, Perenchyma (•ff^fa, a sac). Starch exists in the 

 form of granules, which are minute cells (perhaps nuclei, as Miilder 

 states), in which nutritious matter is stored up. This matter may be 

 deposited in such a way as to give the appearance of striae surrounding 

 a point or hUum, which is considered as an opening into the cell. 

 Allman says the starch granule consists of a series of lamellae, in the 

 form of closed hollow shells, included one within another, the most 

 internal inclosing a minute cavity filled with amorphous amylum. 

 The concentric striae visible on the granule indicate the surface of 

 contact of these lamellse, and the so-called nucleus of Fritsche corre- 

 sponds to the central cavity. The external and internal lamellse differ 

 in consistency, and in other conditions of integration. The lamellse are 

 deposited centripetally. The starch granule differs from a true vege- 

 table cell in the absence of a proper nucleus, and in presenting no 

 chemical difference between the membrane and the contents. The 

 grains of starch are well seen in the cells of the potato (fig. 34). In 



Fig. 34. Fig. 36. Fig. 36. 



wheat (fig. 35), and in maize (fig. 36), the form of the granules, and 

 the successive layers of deposit, are also seen. The grains in the 

 stem of Nuphar luteum show the centripetal formation, that is, the 

 increase by layers deposited within each other. The addition of iodine 

 causes the grains of starch to assume a blue colour, and marks the 

 difference between them and the walls of the cell containing them. 

 Schleiden affirms that starch is the most widely diffused substance in 

 the vegetable kingdom ; its presence may be regarded as in a measure 

 indicating the age of the cell. With its formation in many cells, we 

 have a limitation of vital activity, by which the organism is brought 

 into such a condition that the power of germination may be preserved 

 for a very long period. 



Ceystals are found in the interior of cells. They probably owe 

 their origin to the union between the acids produced or taken up by 

 plants, as oxalic, phosphoric, malic and carbonic, and the alkaline 

 matter, as lime and potash, absorbed from the soil and circulating in 

 the sap. The crystals usually lie loose in the cells (figs. 37, 38) ; 

 but they are sometimes found in a distinct tissue called a cystolith 

 (xvarie, bladder, and Xi6og, a stone), suspended from the wall of a 



Fig. 34. Cell of Potato, containing striated starch grains. Fig. 35. Grains of starch of 

 Wheat. Fig. 36. Grains of starch of Maize. 



