AND IRRITABILITY OF SENSITIVE PLANTS 227 



14. With transition from the less sensitive to the more sensitive 

 species the cells of the pulvini contain, in increasing amount and com- 

 plexity, aggregation bodies resembling those previously described by 

 Darwin and other investigators, as associated with irrito-contractile 



centers. 



IS.These masses show contraction and aggregation changes under 



stimulation. 



16. From varied chemical reactions (tests for various cell contents) 

 the writer would view the aggregation bodies as being proteinaceous in 



nature. 



17. All irrito-contractile changes, alike during contraction and 

 expansion, seem to be due to changes primarily in the protoplasmic sac 

 surrounding each aggregation body, next in the aggregation body itself, 

 finally in the amount of liquid these may absorb or give off. 



18. In fixation, demonstration and identification of the aggregation 

 masses the most helpful chemical agents were found to be gold chloride, 

 platinic chloride, ferric chloride, ammonium carbonate, silver chloride 

 and silver nitrate, the first two giving a brownish purple to purple 

 color to the aggregation bodies. 



19. The writer agrees with Haberlandt in considering that the 

 complex hairs, often found over the irrito-contractile pulvini, or even 

 over the general leaflet surface, seem to act as delicate receptors of 

 environal stimuli. 



20. Among the varied types examined the two most specialized 

 hairs are those distributed over the leaflets of Desmodium canescens and 

 Mimosa Spegazzini, in the former of which special bundle diverticula 

 pass into the bases of the hairs; in the latter prolongations, from the 

 zone of crystal cells rise up into the bases of the hairs. 



21. All present evidence seems to point to the conclusion that, alike 

 in seedling and adult axes, crystal cells and aggregation masses gradually 

 become fewer in the hypocotyl and are entirely absent in the root. 



22. For all of the above sensitive plants now studied, as for Drosera 

 recorded by Darwin, and Dionaea recorded by Macfarlane, all forms of 

 energy— thermal, luminous, chemical, mechanical, electrical and molar 

 stimuU, can act as stimulants to produce irrito-contractile movements. 



