360 



Tricofxious Races. 



Ljcntianoidcs 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-Plafanus. 

 A tetracotylous seedling, the 

 axis of which spHts 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 



