1905] McCCALLUM—REGENERATION IN PLANTS 107 
minal bud and all the leaves were removed, and the shoots, separated 
from the parent plants, were placed in the dark. The axillary buds 
started to develop and continued until all the nourishment in the 
shoots were exhausted. 
Roots of Taraxacum were cut into several pieces, and on each 
piece new shoots arose. We cannot say that each piece was either 
better or more poorly nourished than before. A Marchantia thallus 
grown in very weak light and plainly in a™semi-starved? condition 
regenerated when cut across transversely. 
It seems clear from the experimental evidence’ that, at“least in the 
plants mentioned, there need be no increase“in nutritive conditions to 
occasion regeneration, and we mustjlook”elsewhere for the stimulus. 
DISTURBANCE IN WATER CONTENT. 
When the leaves or other transpiring surfaces of a plant are 
removed, there is often opportunity for a better supply of water in 
the remaining parts. The profound{influence of water as a factor 
in growth is too well known to need jemphasis. If the leaves of many 
trees or shrubs be removed early enough, the axillary buds will 
develop shoots instead of remaining dormant until the next year. 
DECANDOLLE (1) attributed this to the “sap” being no longer drawn 
away from the buds by the leaves. W1esNER (15) thinks that the 
young buds are hindered from developing”because the water is with- 
drawn from them by the more actively transpiring leaves. In isolated 
pieces of Salix stems V6cuTING (1 3), believes that water is the factor 
that determines the appearance of roots,’ and Kress (5, p. 104) had 
experimentally proved this to be true in at least some species.. WAK- 
KER (14) obtained buds on leaves of Bryophyllum by submerging 
them, and thinks it due to disturbances in the water current. GoE- 
BEL (3, p. 393) obtained budsonSleaves"of Aneimia rotundijolia by 
either submerging them or placing them in very moist air; also on 
uninjured leaves of Cardamine pratensis by keeping the plants in 
Moist air. KxEps attributes this to the checking of transpiration 
and consequent abundance of water in the leaf.. By surrounding a 
Portion of an uninjured stem of Salix by a glass cylinder filled with 
water, KLEBs (5, p. 104) foundfthat roots develop upon that part. 
Other plants, especially those whose natural habitat is in wet places, 
