22 GOURD. [CH. II 



That is to say, they become green, and in gaming 

 chlorophyll they at once endow the young plant with the 

 power of earning its own living, because they give it the 

 power of gaining carbon from the air to be built up into 

 the store of organic material already existing. 



The manner in which the gourd germinates is in some 

 ways unique. The radicle as it emerges from the seed 

 grows downward and fixes itself in the soil 1 . On 

 its lower side a sharp projection or peg grows out as 

 shown in fig. 5. The peg serves to hold down the seed- 

 coat while the cotyledons (with the plumule between 

 them) are extracted. This extraction is effected by the 

 growth of that part of the primary axis of the plant 

 which is just below the cotyledons, and which is known 

 as the hypocotyl. A simple proof that the peg is really 

 of value may be got by removing that part of the seed- 

 coat on which the peg should act; when this has been 

 done the cotyledons remain in the seed; although they 

 are finally freed by their own growth bursting the testa. 



When the arched hypocotyl has made its way through 

 the soil it straightens itself, and points vertically upwards ; 

 the cotyledons increase in size, develope chlorophyll and, 

 instead of remaining face to face, open out and take up a 

 roughly horizontal position, thus exposing their upper 

 surfaces as efficiently as possible to the light. The 

 plumule then begins to increase vigorously and the plant 

 soon grows out of the stage in which it can be called 

 a seedling. The most striking feature in the developing 

 plumule is that it bears leaves having no resemblance 

 1 See the account of Geotropism in Ch. III. 



