112 THE AMERICAN BOTANIST. 



than storehouses. Water, however, is as much a plant food as 

 is starch, so these tubers, after all, act as food storage organs. 

 The reason they contain water instead of starch is probably- 

 due to the fact that N. Cordifolia is an epiphyte and therefore 

 more subject to drouth than many other plants. The habit 

 of producing these tubers is common to several species of the 

 genus, notably N. tiiberosa, N. Philip pinensis, N. pluma, N. 

 undiilata and N. Baiisii. Our common A^, exalta does not pro- 

 duce them. — Fern Bulletin. 



A Plant Sense Organ. — The unsentimental botanist is 

 likely to set himself pretty solidly against any suggestion that 

 plants have feelings or nerves, and yet these organisms often 

 behave in ways that are wonderfully like the actions of ani- 

 mals under similar circumstances. The growth of roots toward 

 moisture, for instance, seems dictated by reasoning faculties 

 in the plant, and the circumnutation of plants, by means of 

 which a climbing vine reaches about until it finds something 

 to climb upon is another illustration of allied phenomena. In 

 most cases, however, it is comparatively easy to show that 

 these apparent responses to conscious cerebration are brought 

 about by purely physical processes. One of the more recent 

 discoveries in this line is in connection with the response of 

 roots to gravity. It is well known that the first root goes 

 downward in response to this force and the inference is often 

 made that gravity pulls it down, quite forgetful of the fact 

 that other roots do not grow downward, and that the main 

 root does not do so under certain circumstances. It is found 

 that the root distinguishes gravity by means of certain free 

 starch grains in the cells of the root-tip. No matter in what 

 position the root may be these starch grains fall to the bottom 

 of the cell and in this way indicate the downward direction. 

 This, however, comes exceedingly close to being a sense-organ 

 such as animals possess. 



