328 



Transactions of the Canadian Institute. 



[Vol. VII. 



palisade tissue and spongy parenchyma are affected, — including the 



guard cells of the stomata, — 

 in a manner which is quite 

 noticeable and important 

 (Fig. 13). Outside of this 

 green ring is seen one slightly 

 lighter in colour. This is 

 probably due to the fact that 

 an extra supply of nourish- 

 ment is now required by the 



enlarged and more active cells in the green ring, and these cells outside 



the ring are drawn upon to furnish this supply. 



1 



FIG. .3. 

 Surface view of guard cell of tobacco leaf. A, from 

 area P, Fig. 12 ; B, natural condition ; C, from area 

 Q, Fig. 12. 



In experimenting upon Chilomonas, an infusoria, W. E. Garry, 

 (1899, p. 291) shows that when certain solutions are allowed to diffuse 

 gradually toward the colony, a ring of the animals appears. This ring_ 

 formed by the crowding of the animals, gradually widens, and with some 

 solutions, after a time, recedes. This would tend to show that the ring 

 is formed of animals, not only those driven away by the irritating liquid, 

 but also of those attracted towards it. In fact H. S. Jennings goes so 

 far as to state that Paramecia are negative to strong acids and positive 

 to weak acids. Whether this offers any explanation to the condition of 

 the leaf around the spot it is not easy to say. At all events the 

 phenomena are similar and in both cases exceedingly remarkable. 



The diagrams here given are self 

 explanatory, and are intended to 

 illustrate the general appearance of 

 the spot upon the leaf several days 

 after the application of the alkali 

 to the surface, to show the effect 

 upon the stomata and upon the 

 general tissue of the leaf. The 

 spot does not at first appear light 

 coloured but rather of a rusty 

 brown, gradually becoming lighter. 

 It was also quite noticeable that 

 the thickness of the leaf was 

 somewhat less in the case of 

 cured tobacco leaves, some dis- 

 tance away from the spot than it 

 was in the centre of the spot. 



CI 



' <5.3. 



Ca 



IG. 14. 



Tobacco leaf showing spot. Ci , deep green 

 ring; C 2, dead area; C3, tissue from region 

 of O, Fig. 12. 



