1902.] Influence of an Excess of Carbon Dioxide on Plants. 421 



The only feature of anatomical difference in the stems of the two 

 series consisted in the inferior differentiation of secondary wood in the 

 C0 2 plant, whilst the phloem was equally well developed in both. 



The roots were perfectly similar in the two series. Starch occurred 

 in much larger quantity in the leaf, and ground parenchyma of the 

 CO-2 plant than in the control example. Crystals of calcium oxalate 

 occur in the leaves of both series, and appeared to be about equally 

 distributed over equal areas. 



Fia. 5. Fuchsia, sp., epidermis from lower surface of leaf. A, air-; B, C0 2 -plant. 



The results upon the structure of flowering plants, consequent on 

 increasing the amount of carbon dioxide normally present in the 

 atmosphere to about three and a half times this amount (i.e., when it 

 is present in the proportion of about 1 in 1000 volumes) may be 

 briefly summarised as follows : — 



1. The growth of the internodes is checked, and the period of 

 growth as measured by the elongation of successive internodes is 

 lengthened. 



2. The growth in surface of the leaves is arrested at a more or less 

 early stage. 



3. The absolute number of stomata per unit area of leaf surface is 

 considerably increased, largely or entirely as the result of the non- 

 attainment by the epidermal cells of their normal size. The guard 

 cells of the stomata do not however share in this diminution, but are, 

 if anything, larger in plants treated as above. The guard cells also are 

 gorged with starch, and the stoma remains open even when the leaf is 

 killed in spirit. The relative proportion of the stomata to the number 

 of epidermal cells in a given area, remains approximately constant 

 for both leaves treated with the additional carbon dioxide, and those 

 which have been grown under normal conditions. But although the 

 stomata show the increase in number just referred to, their total 

 number on the whole surface of a treated leaf may be smaller, on 



