1902.] Influence of an Excess of Carbon Dioxide on Plants. 417 



appearance on the part of the C0 2 plant is also manifested by this 

 species. 



Comparing the total average length of the five youngest internodes 

 in each specimen, the proportion was found to be 1*00 : 0*65, but 

 nearer the base of the specimens this relation was reversed. The 

 amount of material at our disposal did not, however, enable us to 

 determine whether this is to be regarded as an accidental variation, 

 though we incline to think it is not so. Possibly it may be connected 

 with the fact, which obtains here, as in KalancJioe, that the full size of 

 internode is reached sooner in the control than in the C0 2 plants. 



The stem and leaves are armed with spines which were somewhat 

 more numerous and very much better developed in the normal (control) 

 plants. 



The proportion existing between the size of the leaves in the air 

 and C0 2 plants respectively is 1*0 : 0*6. As regards the anatomical 

 differences these are in the direction such as might have been antici- 

 pated from a consideration of the diminished leaf surface. The xylem 

 is less well developed in the experimental than in the control plants, 

 whilst the phloem again shows but little variation. The hypodermal 

 collenchyma is not so well marked in the C0 2 as in the air plant, 

 exactly as is the case with Kalanchoe. 



The mesophyll of the leaf was somewhat more spongy in the C0 2 plant 

 than in the control, a fact perhaps to be correlated with the greater 

 number of stomata in the former. 



No difference was observed in the structure of the roots of the two 

 series. 



The number of stomata per unit area of leaf surface was greater in 

 the C0 2 than in the air plant in the proportion of 1*0 : 1*3. The 

 relative number of epidermal cells and stomata in the two series was 

 100 : 43 (air) and 100 : 48 (C0 2 ) respectively. 



The cells of the leaves (including the guard cells) and of the wood 

 parenchyma were gorged with starch in the case of the C0 2 plant, and 

 the guard cells of the stomata were widely open as contrasted with 

 their closed position in the control specimen. 



Begonia gracilis. — The relation between the average lengths of the 

 four youngest internodes in the two series is expressed by the ratio 

 TO : 0-5 for the air and C0 2 plant respectively. But the internodes 

 of the latter do not reach their full length as soon as do those of the 

 control plant : in this they resemble the foregoing species. 



The proportionate size of the leaves in the two series is about 

 1-0 : 0-56. 



The stomata in the leaves of this plant are aggregated in groups, these 

 being separated from one another by large epidermal cells, that junction 

 as water-storage elements. The leaves of the C0 2 plant contain a larger 

 number of stomata per unit area than those of the control plant, the 



