R. BRAITHWAITE ON THE HISTOLOGY OF PLANTS. 135 



yariable ; and this, with the position of the nucleus and degree of 

 lamination, afford distinctions for recognising particular kinds of 

 starch. We may distinguish simple and compound starch granules, 

 the former being most frequent, and divisible into rounded, as in 

 the starch of Potatoe, Canna, Graminese, Leguminosae, &c. ; jiatly 

 orbicular in Turmeric and other Zingiberaceag ; rod-shaped in the 

 milky sap of Euphorbias. The compound starch granule usually 

 forms the segment of a sphere, and is met with in Allium and 

 Colchicum, in the root-bark of Sarsaparilla, and in Bryony root. 

 Each starch granule consists of starch substance, water, and a 

 minute quantity of mineral matter ; the former is a carbo-hydrate, 

 agreeing closely with cellulose, and appears in the granule under 

 two modifications, one more soluble, which with aqueous Sol. of 

 Iodine, assumes a fine blue colour (Granulose) ; the other but 

 little soloble, and in reaction coming nearer to cellulose (Starch- 

 cellulose). If the granulose be removed the cellulose is left be- 

 hind as a skeleton of the granule, but its weight is only 2 — 6 

 per cent, of the whole. 



The true structure of the starch granule has been a subject of 

 much dispute. The view long held was, that growth arose by ap- 

 position of homogeneous laminae, deposited over each other from 

 within outward, the dark stride being due to interspaces containing 

 air, and the refraction of light by the edges of the laminae. We 

 observe within the starch granule a centric or excentric nucleus, 

 erroneously called a hilum, and around this the laminae are deposited. 

 Now, Nageli, in an elaborate paper on the subject, states that 

 growth occurs only by intus-susception, and that the appearance 

 depends on adjacent laminae, which are alternately rich in water and 

 anhydrous. The layers increase in thickness and size by internal 

 deposit, then a differentiation is set up, and if it be a dense layer a 

 matter rich in water is deposited in its median plane, and it now 

 becomes spht into two lamellae. Often two nuclei are found in a 

 young granule, round each of which lamellation takes place, and 

 growth being strongest in the line connecting them, the nuclei 

 constantly move further apart, until an internal splitting at right 

 angles to the connecting line leads to the formation of two granules. 

 If this dividing be oft repeated, highly compound granules result, 

 as in the endosperm of Oat and Si3inach, also in the parenchyma 

 of quick- growing plants, as melon-stems and sprouting plants of 

 kidney-beans, in which they are mulberry-shaped. 



