13 



etc. Tendrils are distinguished (from twining- plants) l»y 

 being in a high degree irritable especially to nntiact ici//> a 

 solid body. 



" If a leaf of Mimosa be stimulated by means of the hot 

 focus of a burning glass, not only that leaf folds together, 

 but the stinuilation extends, till all the leaves of that branch 

 have the movement" ! 



"The aiillions of stomata in an average size leaf simulta- 

 neously open when the sun shines on the leaf, and simulta- 

 neously close when it l)ecome8 shaded." 



The leaves of many plants are so sensitive as to close in 

 slightly cloudy weather, as oxalis and anagallis. Numerous 

 flowers close at night and open in the mornino-, etc. 



"We have no necessity to refer to the physiology of 

 nerves in order to obtain greater clearness as to the phe- 

 nomenon of irritability in plants; it will perhaps on the 

 contrary, eventually result that we shall obtain from the 

 processes of irriiabiliff/ in plants data for the explanation, of 

 the pJiysioloyij of nerves."' (J. von Sachs). 



"The irritation set up by insects themselves is one of the 

 most potent causes of a flow of sa[) to certain definite places 

 which encourages local growths. The effects under mechan- 

 ical irritations and strains, of nutritive matters of the same 

 kind, of poisonous substances, of electricity, etc., all show 

 that the bond which unites the animal and vegetable king- 

 doms is of one and the same nature." ( Prof. (ieo. Henslow) . 



"When muscular til)ers are touched by a pointed instru- 

 ment they exhibit contraction even after they have been 

 detached from the body, provided that too long a period of 

 time has not elapsed. At one time it was supposed that the 

 contraction of a muscular fiber depends so completely upon 

 the agency of the nervous system that it might be consid- 

 ered as the direct function thereof ; but a more critical 

 examination of the circumstances of the shortening of the 

 til)er cells, shows that it })ossesses many features in common 



