STUDIES IN PLANT REGENERATION 229 
to pieces of which an equal number were left in the light and in 
the dark for 17 days. At the same time portions of the leaves 
were preserved for microscopical examination. Both sets of speci- 
mens regenerated roots and shoots in that time, those in the light 
being noticeably larger. This result would fall in line with the 
one described by McCallum and might warrant the deduction that 
the regeneration is independent of food. The error of. the con- 
clusion, however, lies in the fact that there was still a considerable 
amount of starch in the leaf at the time of cutting. Sections made 
of the parts which had been preserved showed starch grains scat- 
tered throughout the leaf, but collected sometimes in large num- 
bers in the neighborhood of the veins. This material, therefore, 
doubtless served as the basis for regeneration. 
Experiment 51.-- Leaves of a plant of Begonia Rex which 
was darkened for four and one half days were next treated in the 
same manner. Sections showed still a few isolated starch grains, 
so that even after this lengthy exclusion from the light, not all the 
food previously made had been consumed. However, in this case 
the difference between the two sets of parts was marked. All those 
subsequently exposed to the light formed roots and shoots nor- 
mally, while the ones in the dark decayed without regeneration. 
Experiment 52. — The same result was obtained with leaves 
of a bean plant that had been darkened only 48 hours. Without 
light the leaves did not form even a callus; when set in the light, 
calluses and roots formed, but more slowly than normally. These 
results seem to indicate, therefore, that regeneration does not 
usually take place in the piece during starvation. Consequently 
the question naturally arises as to whether food actually was lack- 
ing in the stem-parts used by McCallum. 
To confirm the result as to the effect of the absence of light, 
parts were also placed in an atmosphere devoid of carbon-dioxide. 
Experiment 53. — The materials used were leaf-portions of Be- 
гота Rex, of two species of Peperomia and of Pelargonium which 
had all been darkened four days before the beginning of the ex- 
periment. These were placed underneath a bell-jar from which the 
carbon-dioxide was removed in the usual manner. None of the 
parts regenerated. Тһе experiment was not so conclusive as the 
preceding ones, however, inasmuch as the apparatus had not been 
