86 . 1. Dachnowxki— Problem of Xei'oinorphy. 



the CO, percentage of the vertical gradient is least and 

 approximates that of the free air ; the comhined effect of 

 the intensity of light and the greater saturation deficiency of 

 the air is provided for by an increased thickness of the 

 mesophyll layer in the foliage to minimize disturbances in 

 the carbon dioxide supply. This and the narrow leaves with 

 restricted stomata confined to deep furrows and, in some cases, 

 protected by hairs, wax, or heavy cuticle, are devices common 

 to plants in bogs where the plants must protect themselves 

 against unfavorable atmospheric influences. The aerial parts 

 of plants are constantly losing water by transpiration, a process 

 similar to evaporation but controlled by the plants within cer- 

 tain limits. To reestablish equilibrium this water loss is 

 replaced by the supply of water from the substratum by root 

 absorption. The taller plants are thus subjected to a difficulty 

 in maintaining the balance between absorption and transpira- 

 tion, in the same manner as are plants living in deserts or in 

 sandy regions. Though the amount of transpiration exhibited 

 by plants is partly influenced by the physical conditions of the 

 atmosphere such as temperature, humidity and wind, yet these 

 factors are much more uniform than are the amounts of avail- 

 able water supply. The limitations of this paper do not per- 

 mit going into greater detail in respect to the nature and the 

 degree of toxicity in bogs, or in respect to the kinds of plants 

 or the parts of plants which are most affected. 



The nearest analogue of the accumulation and the con- 

 ditions of growth for the vegetation of the Coal Measures are 

 the bogs and marshes of to-day. Were there no other trust- 

 worthy records of the occurrence of bacteria and fungi in 

 Paleozoic times,* it would still be a natural supposition that 

 these organisms were abundantly represented, and produced 

 physical and chemical changes in the substratum. The trans- 

 formation products, of whatever nature, checked the activity 

 of the roots of plants and depressed their transpiration. The 

 striking similarity of the aerial shoots of the Carbonifer- 

 ous plants to those of modern times in bogs and undrained 

 swamps restrain one, therefore, from assuming that the atmos- 

 phere differed greatly in temperature and humidity, or was 

 different in the chemical constituents from what it is now. 

 There may have been moderate variations in the carbon diox- 

 ide content of the air, but this would require experimental 

 proof upon bog plants and the group of plants similar to those 

 which lived in Carboniferous times, the scouring rushes, the 

 lycopods, ferns, cycads and gymnosperms, to assign its limits. 

 The statements in current literature as to the strengths of that 



* Renault, B., Recherches sur les bacteriacees fossiles. Ann. Sci. Nat. 

 Bot. (8), ii, 275-349, 1896. 



