BLASTOGENIC VARIATIONS. 155 



is chiefly derived from observations on plants, for by 

 reason of the ease and success with which they are 

 carried out, and the scientific and practical results ob- 

 tained, these altogether outweigh the comparatively 

 few observations which have been made on animals. 

 Though much of the evidence obtained is variable and 

 contradictory, yet some of it has afforded results of 

 striking lucidity. Especially is this the case as regards 

 what may be termed Mendel's Law of Hybridisation. 

 Though discovered as long ago as 1865,* this important 

 generalisation has passed almost unnoticed until the 

 last year or two, when it was independently re-discov- 

 ered and confirmed by De Yries, by Correns, and by 

 Tschermak. Mendel's observations extended over 

 eight years, during which over 10,000 plants were ex- 

 amined. Most of them were made upon the different 

 varieties of the pea, Pisum sativum. The varieties 

 employed differed in respect of (1) the form of the ripe 

 seeds, these being either nearly round, or angular and 

 wrinkled; (2) the colour of the cotyledons, these being 

 various shades of yellow or green; (3) the colour of the 

 seed coat, this being either white, gray, or brown; (4) 

 the form of the ripe pods, these being either simply in- 

 flated, or deeply constricted between the seeds; (5) the 

 colour of the unripe pods, this being yellow, or light to 

 dark green; (6) the position of the flowers, either axial 

 or terminal; (7) the length of stem. 



On uniting each of these two differentiating char- 

 acters by cross-fertilisation, the hybrids obtained in 

 each case were found to resemble only one of their 



* Abhandl. d. naturforsch. Ver. in Brttnn, Bd. iv. 1865. Trans- 

 lated by W. Bateson in J. Roy. Horticult. Soc., xxvi. p. 1, 1901, 



