356 UTRICULARIA MONTANA. [Chap. XV 111. 



twenty, there were all possible gradations between a short 

 length of a rhizome just perceptibly swollen and one so much 

 swollen that it might be doubtfully called a tuber. When 

 well developed, they are oval and symmetrical, more so than 

 appears in the figure. The largest which I saw was 1 inch 

 (25.4 mm.) in length and .45 inch (11.43 mm.) in breadth. 

 They commonly lie near the surface, but some are buried at 

 the depth of 2 inches. The buried ones are dirty white, but 

 those partly exposed to the light become greenish from the 

 development of chlorophyll in their superficial cells. Th^y 

 terminate in a rhizome, but this sometimes decays and drops 

 off. They do not contain any air, and they sink in water; 

 their surfaces are covered with the usual papilla?. The bun- 

 dle of vessels which runs up each rhizome, as soon as it enters 

 the tuber, separates into three distinct bundles, which re- 

 unite at the opposite end. A rather thick slice of a tuber 

 is almost as transparent as glass, and is seen to consist of 

 large angular cells, full of water and not containing starch 

 or any other solid matter. Some slices were left in alcohol 

 for several days, but only a few extremely minute granules 

 of matter were precipitated on the walls of the cells; and 

 these were much smaller and fewer than those precipitated 

 on the cell-walls of the rhizomes and bladders. We may 

 therefore conclude that the tubers do not serve as reservoirs 

 for food, but for water during the dry season to which the 

 plant is probably exposed. The many little bladders filled 

 with water would aid towards the same end. 



To test the correctness of this view, a small plant, grow- 

 ing in light peaty earth in a pot (only 4i by 4J inches out- 

 side measure) was copiously watered, and then kept without 

 a drop of water in the hothouse. Two of the upper tubers 

 were beforehand uncovered and measured, and then loosely 

 covered up again. In a fortnight's time the earth in the pot 

 appeared extremely dry; but not until the thirty-fifth day 

 were the leaves in the least affected; they then became 

 slightly reflexed, though still soft and green. This plant, 

 which bore only ten tubers, would no doubt have resisted 

 the drought for even a longer time, had I not previously re- 

 moved three of the tubers and cut off several long rhizomes. 

 When, on the thirty-fifth day, the earth in the pot was 

 turned out, it appeared as dry as the dust on the road. All 



