512 ON SEEDLINGS 



seed, except, of course, the small portion occupied by the plumule 

 and radicle. 



We have seen that in the fruit of Pterocarya four hollow 

 spaces gradually form themselves in the originally solid fruit, 

 and that into these spaces the seed sends four prolongations, 

 into which again the cotyledons subsequently grow. Now in 

 the Walnut a very similar process takes place, only the hollow 

 spaces are much larger and confluent with the ovarian cavity, so 

 that instead of a solid wall with hollow spaces occupied by the 

 seed, it gives the impression as if the seed were thrown into 

 folds occupied by the wall of the fruit. To occupy these spaces 

 fully, the cotyledons themselves were thrown into folds as we 

 now see them. The fruit of Pterocarya is much smaller than 

 that of the Walnut, the ancestors of which doubtless had a 

 smaller fruit. As it increased, the cotyledons became fleshier 

 and fleshier, and found it more and more difficult to make 

 their exit from the seed, until at last they have given up 

 any attempt to do so. Hence the curious folds, with which 

 we are so familiar, are the efforts made by the original leafy 

 cotyledons to occupy the interior of the nut. 



Comparison of the Fruits of Pterocarya and Juglans. Thus, 

 then, while essentially similar, the fruits of Pterocarya and of 

 the Walnut offer several remarkable differences. They resemble 

 in some respects the relations between the fruits of the Horn- 

 beam and of the Beech. The fruit of Pterocarya, like that of 

 the Hornbeam, is winged, which is not the case with the Walnut 

 or the Beech ; it is in the two former smaller, and a great 

 deal harder than in the two latter. Again, the cotyledons of 

 Pterocarya are aerial, while those of Juglans no longer perform 

 the functions of leaves and never quit the seed. 



In the Walnut, as in some other trees, it is an advantage 

 that the seeds should be large rather than numerous. In this 

 way they are able to contain a supply of nutriment, which 

 suffices rapidly to carry the young plant above the grasses and 

 other low herbage. These seeds form the food of squirrels and 

 other animals, which accordingly serve to disperse them, and 

 thus perhaps they are enabled to dispense with any other 

 means of transport. Moreover, for such large fruits wings 

 would perhaps be scarcely adequate. 



