38 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



Studies were also made by Strasburger of the starch of Cycas drcinalis. In the rela- 

 tively large part-grains, each grain consisting of 2 to 8 parts, which constitute a single 

 grain, a radial structure was also observed. Likewise in the centric, oval grains of Phase- 

 olus vulgaris a radial structure of the lamellae was observed. In Phaius the starch-builders 

 are rod-like and easily seen, and from them the starch-grains project. The entire starch- 

 grain or only the base was observed to be covered by a delicate membrane separate from 

 the main mass of the starch-builder, and the lamellse extended only to this membrane. 

 Between this membrane and the mass of the starch-builder was a less dense substance, 

 described by Schimper as being a delicate and more or less swollen layer of the starch- 

 builder which borders on the grain. 



Some of the grains, Strasburger found, do not originate in the chlorophjd bodies and 

 starch-buUders directly, but in the cell-plasma. Such grains were observed in the macro- 

 spores of Marsilia (water fern), and the grains were remarkable for the fact that each 

 was covered with a network. The formation of the starch in these macrospores only 

 begins after the macrospore has been developed. The grains are embedded in the proto- 

 plasm, and no speciaUzed starch-buUders are present. These grains, he states, grow by 

 apposition. Starch-grains in the cells of the medullary rays of Conifers are also produced 

 without the agency of starch-buUders. In Pinus sylvestris the formation of starch begins 

 4 or 5 cell-lengths from the cambium. In the cells of the rays at this point very small 

 starch-grains appear in the strands of the plasma-network, and appear to come directly 

 from microsomes. When the grains become larger they lie in the meshes of the network, 

 and have microsomes attached to their surfaces. In principle, the process of starch- 

 formation in Marsilia, Pinus, etc., was not found to differ essentially from the formation 

 in starch-builders, since in both cases protoplasm and mircosomes are utilized in the 

 process. Where starch-builders are present there is merely a more extended division of 

 labor in the protoplasmic cell-body. 



Strasbm-ger states that it is evident that all eccentric grains originate from differ- 

 entiated starch-buUders, and that the eccentric structure is a result of unilateral deposi- 

 tion on the starch-grain, which explains at once the presence of the starch-builder at only 

 one end of the grain. Not all centric grains, however, originate without the agency of 

 starch-builders, because a uniform growth on the entire outside of the grain is possible 

 only so long as the grain is entirely surrounded by the substance of the starch-builder. 

 Finally, that compound starch-grains originate by the union or fusion of grains originally 

 isolated can be established, Strasburger states, in grains of Marsilia diffusa. 



In further studies of the structure of the starch-grain, Strasburger records that up 

 to that time (1882) the lesser density of the interior of the starch-grain had not been satis- 

 factorily explained. He compares the lamellse of cell-walls and starch-grain, and notes 

 that in cell-walls the inner constantly growing lamellse wliich border the cell-contents 

 behave differently from the lamellse of the membranes which are removed from the cell- 

 contents. Every lamella, as it becomes covered by later-formed lamellae, decreases in 

 its refractive capacity, this decrease being due to an increase in the water-content. The 

 same relation holds good for the starch-grain. The lamellae deposited on the outside of 

 the grains becomes less refractive but richer in water as they become farther separated 

 from the outer surface. The parts of the grain which cease to increase, on wliich no new 

 starch is deposited, retain their original density, and their density even increases with 

 age. The anterior or acute end of the very pronounced eccentric Phaius grains is dis- 

 tinguished by its density, and it rejiresents the oldest part of the grain. On account of 

 the increased water-content as the lamellae lie farther from the surface layer, a })ulling or 

 state of tension is created in every lamella, and the tendency is to distribute this strain 

 and thus increase the size of the entire starch-grain, and hence on account of the strain 

 in the inner lamellae, the storage of water in them is favored. This water-storage he con- 



