ORIGIN OF CONDUCTING TISSUES. 1G9 



Guignard, he noticed the not infrequent effect of a rapid 

 chang-e of colour in the perianth after pollination, although 

 it did not fade for a week. The swelling began on the 

 second day in the " gynosteme," and progressed towards the 

 ovary. From having been four centimetres long on the day 

 of pollination, December 4th, 1885, by the 15th of ^pril, 

 1886, it had grown to seven centimetres. The ovules, how- 

 evei', were not full grow^n, the embiyo-sac having still its 

 primitive nucleus ; by the 15th of May, the ovules had 

 attained their complete development. By the 1st of June, 

 fecundation had taken place in nearly all the ovules. Hence 

 about six months were required for the process. 



In this species the spaces over the mid-ribs were covered 

 with long hairs, corresponding to the papillge in Vanilla. In 

 both they appear to have grown after, and as a result of, 

 pollination.* 



In a flower oi Angrrecum superhum which became arrested 

 the influence of the pollen-tube was remarkably illustrated. 

 Three weeks after pollination an arrest of development 

 followed in the ovary ; it had sensibly increased in diameter 

 in the upper part. On examining the ovarian cavity at the 

 top, M. Gruignard found only a small number of jjoUentubes, 

 relatively short in length. f 



Another abnormal case was a Vanilla, in which, from 

 some unknown cause, only two bundles of pollen-tubes were 

 formed on either side of a placenta. Here the ovary grew 

 on that side, causing a strong curvature. On the opposite side, 

 the wall and. the placentas with their ovules were atrophied. 



* Max Wichnra found that silky hairs were sometimes the sole 

 result of his attempts to hybridize willows ; and as analogous instances 

 are the clothing the interior and exterior surfaces of galls with papillae 

 or hairs, an indirect result of the irritation set up by the pupae (p. 138). 



+ A like interpretation may be given to Vegetable Marrows when 

 they swell only at their distal end. 



17 



