tuber formation in Oxalis, but the internal forces are 50 
1899 | CURRENT LITERATURE 437 
finally four tiers of roots were developed. Each year the plant started later 
and later, and for a long time the leaves remained yellow, showing the 
difficulty the plants had in conducting materials up through the series of root 
tubers. The fifth year the struggle was too severe, and the plant died. 
These tubers did not develop buds and were hence incapable of propagating 
the species, but experiments showed that decapitated budless tubers can 
remain alive and fresh for several years. The Dahlia tubers developed a 
stem structure like those of Oxalis. 
One of the most plastic plants employed was Boussingaultia baselloides, a 
plant with the potato type of tuber. This plant grows readily from cuttings, 
roots and rhizomes springing from the subterranean buds, and green shoots 
from the aerial buds. When cuttings are placed in the soil so that all buds 
are in the light, the base of the stem itself, z. e., the buried internode, swells up 
intoa tuber; if the base of the internode lies deep, the tuber is elongated, if 
shallow, it is shortened, showing the restricting influences of light in tuber 
formation. As in Dahlia, these tubers are budless and remain fresh and living 
fora year or two, but cannot propagate the species. The change in struc- 
_ ture is similar to that in the Oxalis petiole which becomes a tuber. A leaf of 
Boussingaultia when placed in the soil gives off roots, one of which swells 
into a budless tuber; these tubers live and function if a shoot is grafted upon 
them. (Leaves of Gloxinia root similarly but develop buds and are capable 
of growth.) The experiments on this plant and on Oxalis seem to show a 
strong inclination toward tuber formation, an inclination which must be sat- 
isfied in one way if notin another. In 7, ‘Aladiantha dubia, a tuberous mem- 
ber of the melon family, the author succeeded in setting out a tendril and 
developing a starchy tuber from its base, which remained fresh long after the 
tendril died. ; 
Véchting carried on several experiments for the purpose of showing the 
influence of external factors, especially light and darkness, upon tuber forma- 
tion. The restricting influence of light in the case of Dahlia and Boussin- 
Saultia has already been indicated. In the radish the tuber is partly root but 
mostly hypocotyl. Plants with all the hypocotyl and part of the bra oes 
the soil tended to develop elongated tubes, to which the root contribute . 
ormore ; in some cases all of the tuber was developed from the root. Etio- 
lated seedlings were darkened at various points by tinfoil, and tuberous 
swellings appeared within the darkened areas, but always ag near oi we ian 
Possible. Two or three separate tubers were sometimes developed in 
: wn to facilitate 
way on a sin mperature and drought were sho 
y ingle plant. Low temp strong that they are 
r hand, will warmth and 
In this species also light 
The 
hot effective early in the season, nor, on the othe 
Moisture greatly retard tuber formation in the fall. econ 
'S unable to prevent finally tuber formation, though it greatly © 
