668 SUMMARY OF CURRENT RESEARCHES RELATING TO 



thickening of the cells in the chalazal region adjacent to the megaspore. 

 The development of the embryo is regular and normal ; the suspensor, 

 unlike that of Leguminosae but in accordance with typical illustrations, 

 consists of a single row of cells. Their function is evidently to direct 

 the food supply derived from the embryo-sac to the embryonic root 



Physiology. 

 Nutrition and Growth. 



Influence of Varying Amounts of Carbon Dioxide in the Air on 

 Photosynthesis and Plant Growth.* — H. T. Brown and F. Escombe 

 show that a living leaf is able within certain limits to respond to in- 

 creased amounts of carbon dioxide in the surrounding air, in such a 

 manner as to indicate an approximate proportion between the photo- 

 synthetic work and the partial pressure of the gas. But further experi- 

 ments show that this power of responding to increased amounts of carbon 

 dioxide is not correlated with increase in dry weight of the plant. The 

 leaf area of plants grown for a long period in excess of C0 2 was 

 generally much reduced in comparison with control plants grown in 

 a normal atmosphere, and in many cases there was a marked inward 

 curling of the leaves. The excess of C0 2 in several cases induced a 

 deeper green colour ; and the leaves showed a much larger accumulation 

 of starch than in those of the control plants. The most striking differ- 

 ences were in the development of the reproductive organs ; flowering was 

 almost entirely inhibited on plants exposed to air containing 11 '4 parts 

 per 10,0U0 of C0 2 . Hence it is evident that the transformation, trans- 

 location, and general metabolism of the leaf-reserves under the altered 

 conditions cannot keep pace with the increased tendency to produce an 

 extra amount of plastic material from the atmosphere. The slight in- 

 crease in the amount of C0 2 in the surrounding air which favours 

 increased photosynthesis, destroys the adjustment of the various parts 

 and results in a more or less abnormal development of the plant, the 

 reproductive functions being especially modified. The authors suggest 

 that the facts recorded by them indicate that the composition of our 

 atmosphere, as regards the carbon dioxide, has remained practically 

 constant for a long period. 



J. B. Farmer and S. E. Chandler f have made a comparative study 

 of the internal structure of the plants of several species used by Brown 

 and Escombe in the above experiments. They find that the results 

 which follow an increase in the amount of carbon dioxide normally 

 present to about three and a half times the amount are as follows: — 



(1) Growth of the internodes is checked, and the period of growth as 

 measured by the elongation of successive internodes is lengthened. 



(2) 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, 



* Proc. Roy. Soc, lxx. (1902) pp. 397-412 (6 pis.). 

 t Tom. cit., pp. 413-23 (5 figs, in text). 



