a _ at rest in the vertical plane of a diameter. Th e glass 
184 BOTANICAL GAZETTE {mw 
of Zea mays (field and sweet corn) are feebly positively rheo- 
tropic. os 
Phaseolus vulgaris, P. lunatus, and P. multifforus produce it 
water better roots than Zea mays, but still show a large percent: 
age of contortion. It will be seen later on that these roots are 
not rheotropic. a 
Tropacolum majus, Pisum sativum, Vicia sativa, and Lathyras 
edoratus also produce many poor roots in water, though 40 pe 
cent. to 80 per cent. will grow straight. oe 
2. Plants insensitive to a stream of water. 
Of the thirty-two species of plants tested for rheotropis™, 
fourteen have shown themselves insensitive to the water-stream. 
These distribute themselves through nine families; while the 
theotropic species number eighteen, and are distributed ae 
_ families. This result shows that rheotropism of roots i 
general phenomenon. In the narrative of experiments which * 
to follow, only those details will be given which are nec’ 
to show the basis of the conclusions reached. a 
_ Three species of water plants, Potamogeton perfola 
canadensis, Ranunculus aquatilis, were brought under 
as follows: From vigorous individuals, apical ; 
S cut, 1o™ or more in length. These cuttings were "7 
upright position to thin glass rods, by tying with : 
pee ‘the glass rods were then fastened by rubber bands 
wood 20™ in length, which was suspended in th 
everal aquaria, thus prepared, were set in a south | 
___ the lower ends of the plants were screened from the ¢ 
_ of the sun. Within a week all plants had sent out 
ae Many adventitious roots, the general direction - f 
_-Vertically downward. The preparations were then | 
centrifuges, and the aquaria revolved, while the 
