26 DIFFERENTIATION AND SPECIFICITY OP STARCHES. 



grains whicli arc surrounded by a common lamellated envelope. A grain of this type may 

 be said to be "half-compound." These part-grains number 2 to 10, rarely 25 to 40, in 

 one grain. If they become relatively large, and the common enveloping layers are thin, 

 a transition tj'pe between the simple and the compound grain is formed. If the lamella- 

 tion becomes rather indistinct, the half-compound grain resembles a single grain, but it 

 can easily be distinguished from the latter by the presence of several hila. Half-compound 

 grains occur usually in grains with eccentric hila. The structure of the part-grains is 

 similar to that of the simple grains. The part-grains of a half-compound grain are usually 

 simple, but rarely are half-compound, each with several hila (see Chapter V). 



In another part of the memoir NiigeU studies the formation of starch-grains in "chlo- 

 rophyl ^•esicles." Starch-grains, he writes, occur not infrequently in the granular or vesic- 

 ular protoplasmic structure of the ceU-contents, but they are constant constituents of the 

 clilorophj^ vesicles. The formation of the grains wdthin the chlorophyl, he found, can 

 often be traced. The grain is described as appearing in a homogeneous green mucus in 

 the form of small points that increase in size and often attain sufficient dimensions to be 

 recognized as starch-grains. In some instances these particles remain rather small, and 

 during their entire development are inclosed entirely by the chlorophyl; in other cases 

 they steadily increase in size, gradually push out through the surrounding chlorophyl, 

 and finally lie free. Grains lying together in the same vesicle may become flattened on 

 their contact surfaces and be united as a compound grain. Such stages of development 

 were observed in the leaf of Begonia dichotoma. In the oval chlorophyl vesicles of Nitella 

 syncarpa 3 to 10 white points were seen and recognized as white starch-granules, very 

 minute in size and not becoming larger. In young cells of Chara hispida the chlorophyl 

 vesicles are arranged in series and are polygonal in shape. They contained 1, 2, or 3, 

 rarely 4, starch-grains, which color blue with iodine. In older cells the chlorophyl grains 

 are considerably larger, with their margins more rounded. In such cells the chlorophyl 

 vesicles are entirely filled \vith starch-grains, containing 1 to 4, rarely 7, starch-grains, 

 which are in contact with each other, and at the surface still covered with a thin layer of 

 clilorophyl. In still older cells the chlorophyl had disappeared entirely. The clilorophyl 

 vesicles are arranged along the ceU-wall, and they are compressed, with the flat surfaces 

 in contact with the cell-waU. 



The starch-grains at first, without coming in contact with each other, lie side by side 

 in the same plane, and they grow chiefly in the plane parallel with the cell-wall, and be- 

 come more or less tabular. Later they touch each other, and their ends become superim- 

 posed upon each other. The j'oung grains are perfectly homogeneous, but later one or 

 more points are noticed which are probably areas where solution has taken place. Chloro- 

 phjd vesicles in the leaf parenchyma of Begonia sp. are perfectly homogeneous at fu'st, 

 and consist only of green-colored protoplasm. After they have increased in size one 

 observes from 2 to 7 shining dots. In still larger chlorophyl vesicles there are 1 to 3, very 

 rarely 6, starch-grains which are recognized by means of iodine. With the growth of the 

 starch-grains the green protoplasm associated with the formation of the grains becomes 

 more and more replaced by starch, and finally instead of protoplasm one observes only 

 starch-grains. In the younger stages the chlorophyl vesicles have 3 to 7 small dots, while 

 among the mature grains none consists of more than 3 part-grains. The explanation of 

 tliis phenomenon is that either an unequal number of starch-grains originates in a chloro- 

 phyl vesicle at different periods of growth, or, as in Phipsalis, some of the points which 

 are visible in the early stages are oil droplets; or it may be that the chlorophyl vesicles 

 divide, as in Chara and Nitella. 



Studies of the solubility of raw starch, and also of the structure of the starch-grain, 

 were made by Jessen (Ann. d. Physik u. Chemie, 1859, cvi, 497), who states that one can 

 easily convince lumself of the solubility of raw starch by crushing the grains of potato 



