104 RUPTURE OF THE SEED-COATS. CiiAt. IL 



same position, relatively to the radicle, as in the 

 figure; consequently it did not rest on the flat tip 

 of the lower half of the seed-coats, but was inserted 

 like a wedge between the two tips. As the arched 

 hypocotyl grew upwards it tended to draw up the 

 whole seed, and the peg necessarily rubbed against 

 both tips, but did not hold either down. The result 

 was, that the cotyledons of five out of the nine seeds 

 thus placed were raised above the ground still enclosed 

 within their seed-coats. Four seeds were buried with 

 the end from which the radicle protrudes pointing 

 vertically downwards, and owing to the peg being 

 always developed in the same position, its apex alone 

 came into contact with, and rubbed against the tip on 

 one side ; the result was, that the cotyledons of all 

 four emerged still within their seed-coats. These cases 

 show us how the peg acts in co-ordination with the 

 position which the flat, thin, broad seeds would almost 

 always occupy when naturally sown. When the tip 

 of the lower half of the seed-coats was cut off, Flahault 

 found (as we did likewise) that the peg could not act, 

 since it had nothing to press on, and the cotyledons 

 were raised above the. ground with their seed-coats not 

 cast off. Lastly, nature shows us the use of the peg ; 

 for in the one Cucurbitaceous genus known to us, in 

 which the cotyledons are hypogean and do not cast 

 their seed-coats, namely, Megarrhiza, there is no 

 vestige of a peg. This structure seems to be present 

 in most of the other genera in the family, judging from 

 Flahault's statements ; we found it well-developed and 

 properly acting in Trichosanthes anguina, in which we 

 hardly expected to find it, as the cotyledons are some- 

 what thick and fleshy. Few cases can be advanced 

 of a structure better adapted for a special purpose 

 than the present one. 



