664 Mutations 



night and day, an irregular jerking movement, 

 which has been compared to the movements of 

 a semaphore. Desmodium is a papiliona- 

 ceous plant and closely allied to the genus 

 Hedysarum, which has pinnate leaves with 

 numerous pairs of leaflets. Its place in the 

 system leaves no doubt concerning its origin 

 from pinnate-leaved ancestors. At the time of 

 its origination its leaves must have become re- 

 duced as to the number of the blades, while the 

 size of the terminal leaflet was correspondingly 

 increased. 



It might seem difficult to imagine this great 

 change taking place suddenly. However, we are 

 compelled to familiarize ourselves with such hy- 

 pothetical assumptions. Strange as they may 

 seem to those who are accustomed to the concep- 

 tion of continuous slow improvements, they are 

 nevertheless in complete agreement with what 

 really occurs. Fortunately the direct proof of 

 this assertion can be given, and in a case 

 which is narrowly related, and quite parallel to 

 that of the Desmodium, since it affects a plant 

 of the same family. It is the case of the 

 monophyllous variety of the bastard-acacia or 

 Bobinia Pseud-Acacia. In a previous lecture 

 we have seen that it originated suddenly in a 

 French nursery in the year 1855. It can be 

 propagated by seed, and exhibits a curious der 



