Tho Determinative Action of Environic Factors Upon Neobeckia acquatica Greene. 277 
The fall series of foliar Organs of Neobeckia ranges from broadly 
oblong lanceolate or ovate leaves in the nepionic stages to narrowly 
ovate or lanceolate floral bracts in the senescent stage. The mature 
or adult leaf of the highest type in aquatics is cut into fine thread- 
like divisions, and the mature leaf of terrestrially grown plants is much 
divided with narrow strap-shaped segments (Fig. 4 and 5). The spread 
and size of the nepionic leaves varies with the conditions under which 
tliey are formed. The structure of the mature leaves varies between 
the limits of the two types indicated according to the environment. 
Nepionic leaves show a more pronounced development of the 
lamina on free cuttings than on awakened lateral buds on entire stems, 
on the upper parts of thickened root-stocks rather than on the lower. 
Cuttings placed in water invariably produce nepionic forms immediately, 
but when the water is allowed to evaporate leaving the plantlets growing 
as terrestrials the type of leaf changes gradually from the aquatic to the 
terrestrial type without the Intervention of nepionic forms. Abrupt change 
from aquatic to terrestrial conditions however is followed by the inter- 
position of nepionic types indicative of rejuvenescence. Anchorage of 
floating aquatic plantlets while submerged was followed by modification 
of the aquatic leaves toward the terrestrial types without the inter- 
position of nepionic forms. Anchorage and exposure of the stems to the 
air would occur together under natural conditions, but either may bring 
about the modifications ensuing when the two act together. 
The development of nepionic leaves indicative of rejuvenation 
occurred in terrestrial cultures with the change from cool to warm 
seasons from warm to cool conditions, with rapid changes in the supply 
of moisture either way, and might also be induced simply by the 
increased aeration following stirring of the soil about the roots. 
Aquatically grown plants remained alive when placed in strong 
(10%) Solutions of potassium nitrate, but the aquatic leaves were killed. 
Terrestrially grown plants retained the strap-like divisions of the leaves 
unharmed under the same conditions: the terminal buds remained inactive 
but the lateral buds were awakened unfolding the broadly laminar 
nepionic leaves of the customary type. In this connection it is pertinent 
to call attention to the fact that the aquatic leaves, and the main 
actively growing points would be most easily dehydrated and to an 
injurious extent by the solution. The terrestrial leaves and the lateral 
buds would endure the concentration and in case of the latter undergo 
the changes which constitute the basis of rejuvenation. 
