418 



Dr. J. B. Farmer and Mr. S. E. Chandler. [May 6, 



proportion being 1*0 : 2*3 (fig. 3, A and B). But this large increase 

 of the number in the case of the experimental plant is solely due to 

 a diminished size of the water-storing epidermal cells, whereby a larger 

 number of stomatal groups are included in a given area. There is no 

 average increase of the number of the stomata within a group, and 

 hence the disparity is clearly due to the effect of the additional carbon 

 dioxide in arresting the growth of the ordinary epidermal cells before 

 they have reached their full size. The guard cells are similar in size 

 in the two series, and are not affected in the same way as the rest of 

 the epidermis. 



The anatomical structure of the stem and leaf presents no features 

 of special interest beyond the character of the epidermis just described. 

 The remaining differences were of a minor character, and of too little 

 constancy to warrant any general points of distinction being traced 

 between the two sets of plants. 



No difference was observed between the root structure in the two 

 series. 



The cells of the leaf and of the ground tissue of the stem were 

 densely filled with starch in the case of the G0 2 plant, but not strik- 

 ingly so in the control specimen. Furthermore, the latter was rich in 

 crystals of calcium oxalate, which were absent from the C0 2 plant. 

 This is of some importance, as indicating that probably the lack of 

 starch in the air plant is to be connected with the utilisation of the 

 carbohydrate, which in the other is simply stored up in an insoluble 

 form. A similar relation exists in the other species in which these 

 crystals occur. 



Impatiens platypetala. — The proportion between the sizes of the 

 leaves in the air and C0 2 plants was found to be 1*0 : 0*76. Owing 

 to the difficulty encountered in securing suitable preparations of the 

 epidermis, no estimates were arrived at as to the comparative numbers 

 of stomata. 



As regards the internal anatomy, the relation between the relative 

 development of the conducting elements of the xylem showed, as was 

 to be expected, the same kind of difference as in the case of the 

 plants already described. In the leaf, the CO2 specimen had the 

 advantage in thickness and in the size of the cells. The contrast was 

 most striking in the palisade layers, which were distinctly double in 

 the experimental plant, as compared with the slight elongation 

 characterising the cells of the corresponding layer in the control 

 plant (fig. 4, A and B). The intercellular spaces were also larger and. 

 more numerous in the former. 



The cells of the C0 2 plant contained very large quantities of starch, 

 as in the examples previously described, and crystals of calcium 

 oxalate also occurred, though not so abundantly as in the tissues of 

 the control plant. 



