AND IRRITABILITY OF SENSITIVE PLANTS 225 



Aggregation bodies in the puh'ini of the various sensitives become 



relati\ely more abundant, are larger and more uniform in size as one 



passes from the less sensitive to the highly sensitive plants. In such 



plants as Oxalis corniculata, O. floribunda and Amphkarpaea monoica 



aggregation is not as pronounced as in more specialized plants like the 



Biophvtums and the Mimosas. Cassia chamaecrista represents a good 



intermediate t\pe. In the Cassias aggregation is observed in the cells 



of the terminal portion of the petiolar gland as well as in the cells of 



the puhini. In feebly sensiti\e plants like Gleditschia or species of 



Oxalis when sections of the puhini are treated with, e.g., gold chloride, 



or ferric chloride, it is observed that the aggregation bodies form slowly, 



being small at first, and are often irregular, such as Darwin noted in 



Drosera. Very often a number of small masses may be present in the 



same cell. These smaller masses may coalesce and form a large body. 



In the highly sensitive plants the aggregation masses form almost 



instantly when treated with the \arious chemicals mentioned above. 



Nature of the Aggregation Bodies, various chemical tests were used as 



to the to determine if possible the nature of the aggregation substance. 



These tests indicate that the masses are proteinaceous in nature. The 



xanthoproteic test gives a positive protein test. Osmic acid stains the 



masses a grayish-black, changing to a deep black. This suggests that 



a fat or lipoid body may be present in the aggregation masses, but 



other characteristic tests for fats, such as staining with alkannin gave 



negative results. 



The aggregation masses are readily soluble in 95% alcohol, con- 

 centrated caustic potash, and glacial acetic acid, but are resistant to 

 concentrated nitric and concentrated sulphuric acids. 



Summary of Result 



1. In geographical distribution it is shown that sensitive plants are 

 very rare in cold temperate regions, become more abundant in warm 

 temperate and sub-tropical regions, and attain their climax of develop- 

 ment alike in number of species and high degree of sensitivity, in the 

 tropics. 



2. The majority of the highly sensitive species are natives of sub- 

 tropical and tropical America, from the Southern States, through 

 Mexico, Central America, tropical and sub-tropical South America. 



3. The most wide spread irritable response shown by these is the 

 nyctitropic, or so-called sleep movement, which has in all probability 

 been induced by rapid changes in temperature, transpiration and 

 radiation effect in transition from day to night. 



