360 
Tricotylons Races. 
gcntianoides the cleft forms gave a mean of 2. 8%, but 
the tricotyls a mean of 2.9%. On the whole, therefore, 
there are no essential differences in hereditary capacity 
between the hemi-tricotylous and tricotylous examples 
of the same races. Moreover we shall see later that this 
rule must be true, when we 
shall find that even the 
atavists in the pure races 
do not differ essentially 
in these values from the 
tricotyls (see 6). 
We now come to the 
tetracotyls. Experiments 
here meet with the diffi- 
culty of distinguishing the 
true types from others. 
For, occasionally, double 
seedlings or twins occur. 
In these the axis is more 
or less deeply cleft; it 
looks as if two seedlings 
had fused together side 
by side. If the cleavage 
extends downwards into 
the hypocotylous region 
there are two separate 
groups of seed-leaves and 
these are frequently at 
Fig. 70. Acer Pseudo-Platanus. 
A tetracotylous seedling, the 
axis of which splits above the 
cotyledon. In the cleft two 
leaves are seen, the lower part 
of whose stalks are grown to- 
gether, back to back. (Spring, 
1887). 
different heights. There 
is obviously no danger of confusing such cases with 
tetracotyls, although the twin seedling does actually bear 
four seed leaves (Fig. 71). But if the division affects 
only the part of the axis above the seed-leaves, these 
