FOLIAGE-LEAVES AND THE CHLOROPHYLL FUNCTION. 543 
alteration of the time of deterioration by the removal of con- 
current members, conclusively discredit such a theory. These 
conditions, together with the fact that the leaves are in a state 
of hunger, point more especially to the conclusion that the 
destruction of the leaf is due to insufficient nutrition. Further- 
more, such deterioration does not always occur earlier in plants 
in the light than in those in darkness, as Jost concludes. It must 
be added in this connection that it is not impossible that the 
regulatory mechanism may play a part in the diversion of 
plastic material or withdrawal of protoplasmic substance from 
the leaves. In this case, however, the disintegration would 
accompany, lustead of precede, the disintegration. 
Incidentally to the results discussed above the following 
conclusions are sustained :— 
Ist. Material constructed in active chlorophyll areas and 
stored in special organs may be transported to inactive chloro- 
phyll-bearing organs in some plants in light and in darkness, and 
be used in such manner as to allow of the perfect development 
of these organs. 
2nd. The removal of concurrent members in darkness may 
have no effect, may cause an exaggerated development of the 
petioles, or may result in the perfect development of the entire 
leaf. The nature of the regulatory mechanism in each instance 
must be entirely specific. 
8rd. It is possible for some plants to form perfect leaves in 
darkness, some when a portion of the stem only is darkened, 
and others when the entire plant is etiolated. It is thus shown 
that no invariable connection exists between the phototonic 
condition and leaf-development. 
4th. The conclusion of Jost, that pathological conditions 
ensue more quickly in inactive leaves in light than in darkness, 
is not capable of general application. The deterioration in 
certain plants appears as quickly in darkness as in others in 
light. 
5th. Placing a leaf under such conditions that it cannot con- 
struct food-material sets in motion the specific regulatory me- 
chanism of the organism in such manner that the plastic material 
may be withdrawn and the organ cast off. An exaggerated 
development of the petioles may be induced in darkness by this 
mechanism. 
