THE STOKAGE OF KESEBVE MATEEIALS 237 



along its axis. As the deposition proceeds the leucoplast 

 becomes very much stretched longitudinally, till its centre 

 is reduced to a thin film round the rod of starch, while 

 what is left of its substance is accumulated at the two ends. 

 The further activity of these portions results in the develop- 

 ment of the two heads of the dumb-bell, the thin film 

 connecting them ceasing to deposit any starch along the 



centre of the rod. 



It is not very easy to 

 see the leucoplasts in the 

 potato ; they can be de- 

 D tected, however, more easily 



Fio. 111. LATICIFEROUS CELL 

 FROM Euphorbia, CONTAINING 



DUMB - BELL - SHAPED STARCH 



GRAINS. 



FIG. 112. GROUP OF ROD-LIKE 

 LEUCOPLASTS, I, EACH BEARING 

 A STARCH GRAIN, s, COLLECTED 

 ROUND THE NUCLEUS, H, OF A 

 CELL OF THE PSEUDO-BULB OF 

 AN ORCHID (Phajus grandifolius). 

 X 500. (After Schimper.) 



in other plants. Fig. 112 shows a group of them forming 

 starch grains in a cell in one of the orchids. The greater 

 bulk of each lies on the outside of the grain ; they are 

 disc-like in shape and not round or ovoid as in the potato. 



In the temporary reservoirs which we have already 

 noticed, such as pollen grains and tubes, the sheaths of 

 cells in various regions of the stem, the tissue of the style of 

 the lily, &c., the deposition of starch is not caused by leuco- 

 plasts but by the general protoplasm of the cell. In these 

 cases immense numbers of very small grains, hardly larger 

 than mere specks, make their appearance, while the highest 

 powers of the microscope fail to' t enable an observer to detect 



