44 DIFFERENTIATION AND SPECIFICITY OP STARCHES. 



The form and size of the grain are determined by the form and number of the chloroplasts 

 attached to the grain. Frequently two or more grains were noted to appear simultaneously 

 in different parts of the chloroplast, when a compound grain results. 



Dodel then takes up the question as to whether or not the grains are formed by the 

 attached chloroplast, and to answer this he studied the half-grown grains in a section of 

 a stem of Pellionia that had been in absolute alcohol for several months, and in which 

 the starch-builders had become decolorized. A section was washed in distilled water, and 

 stained with a weak solution of methyl-violet, when it was found that the half-grown grains, 

 besides being partially surrounded with the hood-shaped chloroplast, were inclosed by a 

 very thin, colorless plasmic layer. In the mature grains this layer was no longer evident. 

 Frequently several chloroplasts were in contact with one starch-grain, this being due to 

 the division of the original chloroplast. The starch-builders increased in mass as long 

 as the starch-grains continued to grow. The lamella of the grains of Pellionia were not 

 perceptible until a comparatively late stage of development. The young grains, as long 

 as they were spherical, appeared to be homogeneous. It is very striking, he states, that 

 the part of the grain about the hilum, which is the oldest, is not lamellated. The solution 

 of the starch-grains, he found, takes place on the entire surface of the grain, even on the 

 part covered Avith the choloroplast. During the process of solution the chloroplasts modifj^ 

 their form as the shape of the grains is changed. After a considerable part of the starch- 

 grain has been dissolved the chloroplast may resume its activity, and thus there may be 

 an intermittent activity of the starch-builders. The formation of irregular grains is prob- 

 ably due, he holds, to such secondary activitj^ of the chloroplasts. 



According to Binz, the majority of the starch-grains of Pellionia are simple, and there 

 are both half-compound and compound grains; but the compound grains do not origi- 

 nate by division of the hilum of the simple grain, as Nageli assumed. The simple 

 grains, he states, fall into two sharply defined categories: In the young state the grains 

 are regular (spherical) in form, and inclosed by the green starch-builders. After they break 

 through the chloroplasts they assume an oval form and become eccentric. Binz assumed 

 that it is not the inner constitution of the starch-grain which determines the form of the 

 grain, but the position of the grain in relation to the starch-builder. After the grains 

 protrude from the chloroplasts, the latter are in contact with the grain in the form of a 

 hood, and the growth of the grain takes place at the point of contact. Such grains take on 

 a more or less regular form. The second category of simple grains includes grains of irreg- 

 ular form, representing advanced stages of the regular forms. When the grains are sub- 

 jected to a 4 per cent solution of potassium hydroxide the lamellse become evident. Two 

 kinds of lamellae are noted, one kind being complete, and the other being incomplete and 

 wedge-shaped. The complete or closed layers are few in number and pass entirely around 

 the hilum. These layers are evidently formed when the grain is entirely inclosed by the 

 chloroplast. In every grain the innermost part is stated to be soft and watery, then follows 

 a complete dense layer, then a watery layer, and so on, until the outermost or last complete 

 layer is very dense, and the boundaries between the complete and incomplete layers are 

 very marked. The inner complete layers are not complete in the early stages of the growth 

 of the grain, and are only perceptible after the starch-builder has become ruptured by the 

 extrusion of the grain and has assumed a hood-like form, and perhaps not \'isible before 

 the first of the incomplete layers is deposited. This is a point, states Binz, that has always 

 been used to ojipose the apposition theory of growth, although nothing can be proved by 

 it in such application. It is possible that the layers as such are deposited as a homogeneous 

 mass from the very beginning, and that by subsequent changes, as bj' the varying absorp- 

 tion of water, are rendered apparent. 



Binz agrees entirely with Schimper in that the growth of starch-grains occurs by appo- 

 sition, yet he admits that there are no direct unimpeachable proofs in support of the theory. 



