ORGANIZATION AND GROWTH 207 
theory of organization.’ Sachs assumes that “with differ- 
ences in the forms of organs are connected differences in the 
substances composing them,” and that ‘from principles 
which hold for all sciences we must assume that the differ- 
ences must be derived causally from the differences in 
chemical constitution” (p. 425). “We shall have to assume 
the existence of just as many specific formative substances 
as there are different forms of organs in the plant.” The 
specific morphogenetic substances are affected through 
external conditions, especially gravity and light, ‘so that in 
certain cases the spatial arrangement of the different organs 
is determined thereby.” The monstrous formation of an 
organ at the place where normally another organ should 
exist —as in the case of heteromorphoses—Sachs attributes 
to an absence of the specific substances necessary for the 
formation of the normal organ at this place, and the presence 
instead of the specific formative substances of another organ 
(p. 464). Sachs also explains why any regeneration what- 
soever of roots or stems occurs in plants deprived of them. 
“Why is it that the simple removal of a piece calls forth a 
regeneration of organs at places where this never would 
have occurred without some disturbing influences such as 
the removal of the piece?” (p. 470). The answer is as 
follows : 
I assume that as long as a green-leafed plant with an upright 
stem is nourished and growing, the specific formative substances 
for the root flow from the assimilating leaves to the system of roots 
at the lower end of the stem, while the substances forming the stem 
flow in a similar manner upward toward the growing points of the 
stem and the branches. If a piece is cut out of the stem or the 
root, the cut surface in itself offers a barrier to the further move- 
ment. The specific formative substances contained in it will, in 
consequence, collect in the neighborhood of the two cut surfaces. 
Those substances leading to the formation of roots will collect at what 
1J. Sacus, Arbeiten des botanischen Instituts in Wirzburg, Vol. II (Leipzig 
1882), pp. 452, 689. 
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