25.] 



CHAPTER I. THE CELL. 



Ill 



bwtyricum, Sarcina ventriculi, Bacterium pastorianum) . But, on 

 the other hand, it is not always present in plants which possess 

 typical chloroplastids ; thus, it is absent, for instance, from the 

 Onion, species of Vaucheria, etc. In the case of plants which 

 have other colouring- matters besides chlorophyll, starch may be 

 altogether absent (Cyanophycese, Diatomaceae) ; or it may be 

 replaced by some other substance (most Phaeophycese and Rhodo- 

 phyceae). In these Phaeophyceae and Rhodophycese there occur 

 small colourless granules distributed in the cytoplasm, consisting 

 of a somewhat mucilaginous substance termed paramylon, which, 



FIG. 68. Cells from the endosperm 

 of Ricinus communis ( x 800). A Fresh, 

 in thick glycerine ; B in dilute gly- 

 cerine ; C warmed in glycerine ; J) after 

 treatment with alcohol and iodine ; the 

 grains have been destroyed by sul- 

 phuric acid, the cytoplasm remaining 

 behind as a net- work. In the grains 

 the globoid may be recognised, and in 

 B C the crystalloid. (After Sachs.) 



FIG. 69. Cells of a very thin section through 

 a cotyledon of the embryo in a ripe seed of 

 Pisum sativum the large concentrically strati- 

 fied grains St are starch-grains (cut through) ; 

 the small granules a are aleuron, consisting of 

 proteids; i the intercellular spaces. (After 

 Sachs.) 



whilst it does not usually give the characteristic reaction of 

 starch, is probably allied to it chemically. A further peculiarity 

 of these plants is that these granules seem not to be formed inside 

 the chromatophores, but in the contiguous cytoplasm. 



(3. Fats occur very commonly in the cells of plants as oily drops 

 scattered throughout the cytoplasm. They are more particularly 

 abundant in seeds, in many of which oil is the form in which the 

 non-nitrogenous reserve material is deposited (e.g. Palm, Castor- 

 Oil plant, Rape, Flax, etc.) ; it is also present in some fruits (e.g. 

 Olive). 



