142 



A TEXT-BOOK OF BOTANY. 



grain, as in Pellionia. Starch is changed into soluble carbohy- 

 drates by the aid of ferments and probably other substances, and 

 in this form is transported to those portions of the plant requiring 

 food. The starch in the medullary rays and in other cells of the 



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FIG. 88. A, potato starch grains showing the excentral and circular point of origin 

 of growth, and lamella:; B, maranta starch grains showing fissured point of origin of growth, 

 and distinct lunu-ll.r; (', \\hrat starch Drains showing indistinct point of origin of growth, 

 and lamdl [; I). corn starch grains, which are more or less polygonal in outline and have a 

 3- to s-angled point of origin of growth. 



wood and bark of plants is distinguished by being in the form 

 of rather small rind nearly spherical grains. In rhizomes, tubers, 

 luillis, and seeds the grains are, as a rule, quite large, and possess 



