80 



PART II. ANATOMY AND HISTOLOGY. 



[24 



plants is a matter of considerable interest. Generally speaking, 

 it is confined to plants which possess chloroplastids, though a sub- 

 stance turning blue with iodine has been found to occur, diffused 

 throughout the protoplasm, in certain Schizomycetes (Clostridium 

 butyricum, 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 (Cyano- 

 phycese, Diatomacese) ; or it 

 may be replaced by some 

 other substance (most Phseo- 

 phycese and Rhodophycese). 



/?. Fats occur very com- 

 monly 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 fniits (e.g. 

 Olive). 



y. Proteid Grains, or Ale- 

 juron, are granules of various 

 sizes, oval or spherical in 

 form, which occur in seeds, 

 and are of physiological im- 

 portance in that they are the 

 source from which the em- 

 bryo is supplied with nitro- 

 genous food when the seed germinates. They consIsT'oTlTmTxture 

 of proteid substances belonging to the globulins and the albumoses. 

 They present no indications of structure, and are much larger in 

 oily_than in starchy seeds. 



The proteid grain generally contains a mass of mineral matter. 

 Most commonly this is a rounded body, the globoid (Fig. 54), con- 



FIG. 63. Excentric starch-brains from the 

 tnber of a Potato ( x 800). A A fully developed 

 simple grain, B-E Compound grains ; a f> 

 young simple grains ; c young compound grain. 

 (After Sachs.) 



