230 STUDIES IN PLANT REGENERATION 
set up so as to allow a renewal of the oxygen. Still as a large 
bell-jar had been used to cover the cuttings which themselves were 
small, it is probable that the amount of oxygen would have sufficed 
for regeneration had other conditions permitted. 
Further evidence of the dependence of regeneration upon either 
a reserve food-supply or the ability of the part to make food was 
afforded by white shoots of various plants. 
Experiment 54. — In the variegated Commelina (sp?) among 
the shoots with green leaves and with green and white striped 
leaves, occasional shoots ,арреаг on which all the leaves are pure 
white. Such white shoots were used as cuttings and compared with 
shoots having striped or green leaves. Whereas the latter rooted 
within a week or ten days, the white pieces in repeated experi- 
ments unanimously failed to regenerate. Тһе results obtained 
with Commelina were reinforced by the behavior of white shoots 
of Oplismenus Burmannii (the Panicum variegatum of the gard- 
eners), of Pelargonium (Madame Solleroi), and of some white orange 
seedlings which appeared as sports in the greenhouse. Іп none of 
these species was the white shoot able to form roots. If, however, 
the leaves on the shoot contained even a very narrow green area 
(Commelina, Pelargonium, Oplismenus) the organs were produced. 
It may be argued here that such parts are in a pathological 
condition, and that the failure to root was due to other causes than 
the absence of a food-supply. White variegation is believed to be 
caused by an oxidase,* which when present in quantity prevents 
the formation of chlorophyll in the chloroplast. Except for this 
absence of coloring matter, however, the cells of the white shoots 
showed no microscopical difference from the normal ones. They 
were as rich in evenly distributed cytoplasm, and their nuclei were 
apparently similar. Moreover, the fact that the possession of a 
single green stripe only 1.5 mm. wide enabled the shoot to regen- 
erate seems to point forcibly to the conclusion that it is primarily the 
lack of the food manufactured by the chlorophyll which prevented 
the shoot from rooting. When this green stripe was darkened, as 
was done crudely by coating it with India ink, the regeneration, 
while not prevented, was delayed for from 4 days to a week be- 
yond the average time. 
зк seque perse ето 
* Woods, A. F. The Destruction of Chlorophyll by oxidizing Enzymes. Cen- 
tralb. Bakt. Parasitenk. und Infectionskrankheiten 5: 745. 1 : 
