Chap. XVIII.] RESERVOIRS FOR WATER. 357 



the tubers had their surfaces much wrinkled, instead of be- 

 ing smooth and tense. They had all shrunk, but I cannot 

 say accurately how much; for as they were at first symmet- 

 rically oval, I measured only their length and thickness ; but 

 they contracted in a transverse line much more in one direc- 

 tion than in another, so as to become greatly flattened. One 

 of the two tubers which had been measured was now three- 

 fourths of its original length, and two-thirds of its original 

 thickness in the direction in which it had been measured, 

 but in another direction only one-third of its former thick- 

 ness. The other tuber was one-fourth shorter, one-eighth 

 less thick in the direction in which it had been measured, 

 and only half as thick in another direction. 



A slice was cut from one of these shrivelled tubers and 

 examined. The cells still contained much water and no air, 

 but they were more rounded or less angular than before, and 

 their walls not nearly so straight; it was therefore clear 

 that the cells had contracted. The tubers, as long as 

 they remain alive, have a strong attraction for water; the 

 shrivelled one, from which a slice had been cut, was left 

 in water for 22 hrs. 30 m., and its surface became as smooth 

 and tense as it originally was. On the other hand, a shriv- 

 elled tuber, which by some accident had been separated from 

 its rhizome, and which appeared dead, did not swell in the 

 least, though left for several days in water. 



With many kinds of plants, tubers, bulbs, &c., no doubt 

 serve in part as reservoirs for water, but I know of no case, 

 besides the present one, of such organs having been developed 

 solely for this purpose. Prof. Oliver informs me that two or 

 three other species of Utricularia are provided with these ap- 

 pendages; and the group containing them has in consequence 

 received the name of orchidioides. All the other species of 

 Utricularia, as wejl as of certain closely related genera, are 

 either aquatic or marsh plants; therefore, on the principle 

 of nearly allied plants generally having a similar constitu- 

 tion, a never-failing supply of water would probably be of 

 great importance to our present species. We can thus under- 

 stand the meaning of the development of its tubers, and of 

 their number on the same plant, amounting in one instance 

 to at least twenty. 



