STRUCTURE.] STARCH. Ill 



SECT. VII. Of Amylaceous and other quasi-organic Matter 

 contained in Tissue. 



Inside the tissue of plants, are found various kinds of 

 particles, some of which give colour or its peculiar turbid 

 appearance to the fluids, others their nutritive quality to 

 particular species. 



Of these some are turned blue by iodine, and are therefore 

 regarded by chemists as composed of amylaceous matter or 

 starch ; others are rendered olive-brown by that agent, and 

 many are dissolved by alcohol, whence they are considered of 

 the nature of resins : all are decomposed by cold, and appear 

 to be connected with the function of nutrition. 



1. Of Starch. 



This substance is so common that no plant is destitute of 

 it, and many, like the Potato, have the cells of their tubers or 

 other parts of the stem filled full of its granules. The 

 rhizome of Equisetum is so crowded with them, that when 

 the cells are wounded, the starch grains are discharged with 

 some force, apparently by the contraction of the membrane, 

 so that the grains appear as if in voluntary motion, as long 

 as the emptying the tissue continues to take place. These 

 particles are perfectly white, semitransparent, generally 

 irregularly oblong, sometimes compound, and marked with 

 oblique concentric circles; they are extremely variable in 

 size, some being as fine as the smallest molecular matter in 

 pollen, that is, not more than ad ^ 00 of an inch in diameter, 

 others being as much as - t J QQ or y^-g-. They often form the 

 centre of the grains of chlorophyll, as Mohl has shown. In 

 the milky juice of Euphorbia, they assume the singular 

 appearance represented at Plate II. fig. 19. #., looking like 

 short cylinders enlarged at each end into a round head : 

 double-headed granules of this kind are not as yet found 

 elsewhere ; Morren states that they vary in form in different 

 species of Euphorbia. 



Starch grains of the smallest size have a distinct motion of 



