THE STORAGE OF RESERVE MATERIALS 231 



the latter is an elongated structure, and at first forms a 

 rod of starch 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 development 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 detected, 



FIG. 111. LATICTFEROUS CELL 

 FROM Euphorbia, CONTAINING 

 DUMB - BELL - SHAPED STARCH 

 GRAINS. 



FIG. 112. GROUP OF ROD-LIKE 

 , LEUCOPLASTS, Z, EACH BEARING 



A STARCH GRAIN, S, COLLECTED 

 ROUND THE NUCLEUS, H, OF A 

 CELL OF THE PSEUDO-BULB OF 



AN ORCHID (Phajus grandi- 

 folius). x 500. (After Schiinper.) 



however, more easily 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 

 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 



