346 Tricotylous Races. 
If the variants are rare, they are as a rule normal 
tricotyls; but if they are more numerous the type is 
usually seen to be variable both in the minus and in the 
pins direction. For convenience of expression we may 
regard a tricotylous seedling as having arisen by the 
doubling of one of the two cotyledons of a dicotyledon 
by splitting, just as is so frequently observed in foliage 
leaves. Smaller degrees of the splitting would lead to 
variations in the minus direction; but if the splitting 
affects both cotyledons there arise variations in the plus 
direction, which, if the doubling is complete, result in 
the origin of tetracotyls (Fig. 63 D). A seedling with 
one normal and one split seed-leaf is called a hemi- 
tricotyl; 1 one with two split seed-leaves, or with three 
of which one is split, is called a hemi-tetracotyl. In the 
same way hemi-pentacotyls, and so on, may be found ; 
but the deviations become rarer as they are more remote 
from the pure tricotylous type. 
If we make a collection of all these forms it is easv 
w> 
to construct a continuous series which extends from the 
pure type, on one side, through stages characterized by 
more or less deep fission, to the dicotyls ; and in the other 
direction in a similar manner to the tetracotyls and, if 
the material is extensive, even further, to the pentacotyls, 
and so on. Fig. 64 exhibits such a series derived from 
Ocnothcra hirtella, the unsplit seed-leaf of each plantlet 
being omitted. But obviously even here the forms fig- 
ured are only a selection from a. much more complete 
series. If we imagine those cotyledons which have been 
cut off in these figures to be split also, the series would 
represent the transition from the tricotyls to the tetra- 
cotvls. 
*> 
1 Beri'hte d. d. bot. Ges., 1894, Vol. XII, p. 26. 
