148 NATURAL FERTILISATION. 



the Wood-sorrel, where twenty to thirty ovules have to be 

 fertilised, Von Mohl gives the quantity as from one to two 

 dozen grains in each anther-cell ; in Impatiens it is consid- 

 erably larger ; while in Viola the number of grains is very 

 small. More detailed examination of these closed flowers in 

 different plants will doubtless yield interesting and important 

 results. * 



* See the interesting papers by Hermann Miiller contributed to ' Nature ' 

 during 1875, 1876. Also a series of illustrated papers from the pen of Dr 

 Asa Gray, entitled " How Flowers are Fertilised," in which the various 

 arrangements for securing or for preventing cross-fertilisation are pointed 

 out. These papers were published in the ' American Agriculturist ' for 

 1876. 



