MORPHOLOGY 



75 



starch grains (Fig. 79 C, D) occur in potatoes, together with simple 

 grains. In oats (Fig. 81) and rice all the starch grains are com- 

 pound. According to NAGELI ( 62 ), the compound starch grains of 

 rice consist of from 4 to 100 single grains; those of the oat of about 

 300, and those of Spinacia glabra sometimes of over 30,000. Starch 

 thus formed from previously assimilated organic substances also 

 requires chromatophores for its production. The grains are formed by 

 means of leucoplasts, which are, in consequence, often termed STARCH- 

 BUILDERS. If the starch grain is uniformly surrounded by the 

 leucoplast during its formation it grows uniformly on all sides and 

 is symmetrical about its centre. If 

 the formation of a starch grain should 

 begin near the periphery of a leuco- 

 plast, the grain would grow more 

 rnpicHy on the side on which the main 

 mass of the leucoplast is present and 

 the starch grain thus becomes excentric 

 (Fig. 82). Should, however, several 

 starch grains commence to form at the 

 same time in one leucoplast, they would 

 become crowded together and form 

 a compound starch grain, which, if ad- 

 ditional starchy layers are laid down, 

 gives rise to a half-compound grain. 



It lias been asserted that starch grains are 

 crystalline bodies, so-called sphserites ( K! ), and Fw. 82. LeaeoptaiU from an aerial tubwr 



are composed of fine, radially arranged, of plu 'J us ;/<"<''>' <'"< 

 needle - shaped crystals, which A. MEYER 

 terms trichites. Their stratification, accord- 

 ing to this view, is due to variations in the 



form and number of the crystal needles in the successive layers, 

 other hand, H. FISCHER ( e4 ) has explained the stratification as due to zonal splits 

 rich in water, which originate by contraction taking place in the substance 

 of the grain at some distance from its growing surface. HENRY KRAEMER ( 6o ) 

 holds that a crystalloid and a colloid substance are present, but are united in 

 different proportions in the successive lamellae of the starch grain. In a few in- 

 dividual cases, ARTHUR MEYER has succeeded in showing that the stratification of 

 the starch grains corresponds to the alternation of the periods of day and night, i.e. 

 to the interference which is thus caused in the nutritive processes. The growth of 

 starch grains is also, according to him, affected by the solvent action of surrounding 

 substances, whereby the peripheral layers may be partially removed, and then no 

 longer completely envelop the entire grain. Starch grains are composed of a 

 carbohydrate, the formula of which is (C 6 H 10 3 )n. Most starch-grains consist of 

 amylose and are coloured blue with iodine ; in addition to this they contain, according 

 to L. MAQUEXXK and EUCJ. Roux C 66 ), a mucilaginous substance which they term 

 amylo-pectin. The presence of this substance causes the pasty union of the starch- 

 grains when treated with boiling water or alkalies. The grains swell in water of 

 60-70 3 C., are but little soluble in water at 100 C., but are rapidly dissolved by 



Viewed from the side ; /.', viewed from 

 above ; /.', leucoiilast becoming green 

 and changing to a chloroplast. (x 540.) 



On the 



