202 
Francis Darwin. 
lower side. The engrams of gravity and contact would be 
associated and contact would produce the result originally due only 
to gravity. In this way a plant manufactures its own stimulus—or 
as it may be expressed, discovers accessory guides. 
Another example of association may be taken from the 
germination of a Cucurbita seed. 1 The lateral processor peg grows 
on the physically lower side of the radicle at the junction of the 
root and hypocotyl. The hypocotyl is oval in section, its longer 
diameter being parallel to the plane of the cotyledons. In the great 
majority of cases the flat seeds of the Curcubita must lie on the 
ground with the plane of the cotyledons horizontal. Therefore in 
the majority of cases the peg must develop on one of the flat sides 
of the radicle. Now imagine a seed sown on its edge with the 
radicle horizontal as before but with the plane of the cotyledons 
vertical. The peg will grow on the lower of the two edges of the 
radicle; but what is remarkable is that an outgrowth also occurs 
on both the flat sides. 
The same sort of thing occurs when the seed is sown vertically. 
Here we imagine that since gravity cannot settle on which surface 
the peg shall appear, it grows on both sides. In both these instances, 
the growth of the peg on the flat sides of the radicle may be 
conceived to have become associated with the early stages of 
germination ; so that these stages cannot occur without the result 
following. These cases seem to me difficult to fit into the modern 
point of view according to which a plant is compared to a substance 
possessing certain properties. According to this view, the property 
of a Cucurbita seedling is to produce a peg on the physically 
lower surface of its radicle. But to account for all the circumstances 
we must assume that it also has the physical property of producing 
out-growths on the flat sides of the hypocotyl, when the seed is 
vertical. No doubt one assumption is as easily made as the other. 
But the two assumptions are isolated and sterile. Whereas by 
bringing in the principle of association we might almost have 
prophesied what would take place. I shall return to the Cucurbita 
seedling later, for its peg is an excellent object on which to hang 
discussions of this character. 
Some interesting examples occur in a paper by Massart. 2 In 
describing the germination of the bulb of Ornithogalum he 
mentions (p. 52) that the leaves are parallel as they make their 
1 Noll, Landw. Jahrb. XXX. 
Bull. Jardin Bot. Bruxelles, 1903. 
