178 BOTANICAL GAZETTE [SEP1 EMBER 
were split away from the costa, and both portions cultivated. 
The result was that buds appeared from the costal region as well 
as from the lateral halves, showing that in the whole leaf the 
power to produce buds was only suppressed. Again with refer- 
ence to the power of young and old or fully mature leaves to 
regenerate. Series of leaves from the mature to the very small- 
est that could be dissected from the end bud were subjected to 
culture, with the result that the leaves from ordinary size to about 
half way through the series produced buds and rhizoids in abun- 
dance. Those from this point on to the very minute leaves pro- 
duced only rhizoids, and these mostly from the region of the 
costa. It was evident that the plastic material was not present 
in sufficient abundance to produce a further development, or that 
being an embryonic organ, the young leaf used its available 
supply of food material towards the growth of its own cells. 
So far as I have observed, the leaves of Mnium in nature 
never give rise to rhizoids when still in connection with the 
stem. In order to afford experimental proof of this, whole 
plants were subjected to exactly the same conditions as the 
detached leaves, but no rhizoid productions resulted. Again, it 
might be thought that the formation of rhizoids and buds was 
called forth by the injury to the leaf. That the cutting of the 
leaf is not effective in the production was shown by those 
experiments in which the leaves were cut and still left in con- 
nection with the stem; even in these leaves no new growth 
resulted. Another series of experiments was made in which the 
costa was cut near the base of the leaf while the lateral halves 
were still left in connection with the stem, with the idea that the 
severing of the costa might cut off the path for the transport of 
food material.’ No rhizoid growth was called forth, and hence 
the previous experiments show that nothing but the complete 
separation of the leaves from the stem is able to call forth the 
power of the leaf to regenerate. When the leaf is still in con- 
nection with the stem, the plastic material can be transported to 
other younger and growing parts; in the detached leaf on the 
other hand the escape is cut off, and thus may favor the produc- 
