president's address. 113 



there stated. Wichura was led by his friend Dr. Wimmer (al- 

 ready, from observation, a believer that many doubtful willows 

 were hybrids) to institute a series of experiments extending over 

 the years 1852 to 1858. The mode of procedure was this. The 

 great object being to exclude all pollen but that of one kind, 

 cylinders were made of thin tarlatan, from two to three inches 

 wide and six to twelve inches long, furnished with a string at 

 either end to tie them closely to the branches, and strengthened 

 in the centre to prevent them collapsing. After the artificial 

 impregnation was complete, as soon as the stigma dried and the 

 ovary began to swell, the cylinders were removed, and only re- 

 placed when the seed was ripe, to prevent it being blown away. 

 The pollen was applied with a camel's hair pencil, a separate 

 pencil being used for each kind of pollen. The seeds of willows 

 germinate very rapidly. Wichura says that the cotyledons make 

 their appearance in from twelve to twenty -four hours. I have 

 not myself found the growth of the seeds nearly so rapid as this i 

 In about a month or three weeks the seedlings have become 

 about an inch high. Wichura speaks of sowing in May. I have 

 not found the seed ripe until June. Wichura' s plan was to raise 

 the plants in pots, which could be supplied with water from 

 below. They were allowed to remain till they were some inches 

 high, and then transplanted into the open ground; and thus 

 plants sown in May, he says, obtained a height of two or three 

 feet by the end of summer. I have seen nothing like this, and 

 very possibly the summer climate of the Continent being warmer 

 than ours may account for the difference, for a height of six or 

 eight inches is the most that I have seen in one season. The 

 smaller kinds generally flowered in three years. The arboreous 

 kinds require four years or more. In one instance a plant sown 

 in June produced flowers when ten months old. 



In willows it would appear by Wichura's experiments that in 

 about four years, by artificial impregnation, one species can be 

 converted into another. In the absence of examples we must be 

 content to accept the statement that there was a real conversion 

 of one species into another. I am obliged by limits of time and 

 space to refer you to Mr. Berkeley's paper for very curious details 



