THE PLANT AS A HOST 



903 



basal swelling, and also the formation oi 

 galleries in which the insects subsequently 

 took up their abode ; failing these atten- 

 tions, it was declared that the vegetable 

 invariably died. This has of recent years 

 been entirely disproved, for it has been 

 shown that specimens of Myrmecodia mav 

 be easily raised from seed and grown to a 

 perfect de\-elopment, even if ants are 

 entirely excluded. 



The Yucca plants are natives of America, 

 and when the specimens are in flower a 

 little moth, known as Pronuha yniccasella, 

 may be seen flying round the blossoms. 

 The females of this species spend most of 

 their time in the blooms, where the}' make 

 arrangements for a novel form of egg- 

 laying. The moth starts with the rolling 

 together of a ball of pollen. As soon as 

 this is ready, it is carried off to another 

 flower, where the insect lays an egg at the 

 base of the pistil, by thrusting its ovi- 

 positor down through the soft tissue. 

 This done, the moth mounts to the summit 

 of the style and places the ball of pollen 

 upon the stigmatic surface, thereby ensur- 



ing the fertilisation of the ovules. When 

 the caterpillar hatches, it finds itself sup- 

 plied with food material in the surround- 

 ing tissues ; there the larva will remain 

 until the ripening of the seed, when it 

 eats its way out, crawls to the ground, 

 and then turns to a chrysalis under the 

 surface. 



As a general rule the numerous galls 

 which are found so abundantly on the 

 Oak, and also on certain other trees and 

 plants, cannot be said to be harmful to 

 the vegetable. Now and again, when the 

 insects producing them become very 

 abundant, growth may be stunted by 

 the presence of the galls ; or, as in the 

 case of the dreaded Grape Louse of 

 Southern Europe {Phylloxera), the plant 

 perishes under the attacks which the 

 minute creatures make upon it. Mostly, 

 however, the plants seem to be neither 

 better nor worse for having to develop 

 the little houses in which the insects find 

 a residence. Everyone must be familiar 

 with the large round " gall nuts " which 

 are found on the twigs of the Oak. Whilst 



THE DODDER (CC'6CC/.I EPITIIYMUM) ON HK.MHKK. A COMMON BRITISH PARASITE. 



