1910] The Ottawa Naturalist. 205 



main problems that confront the student of plant ecology and 

 also the practical value of the study over and above its mere 

 scientific interest. He then proceeded to demonstrate the fact 

 that the minute structure of the internal parts of plants may 

 reveal an adaptation to their environment no less marked than 

 does their external form or habit of growth. The ability of 

 plants to meet the exigencies of a new environment by a modifica- 

 tion of their internal structure was clearh^ shown as in the case 

 of Ranunculus aquatilis and Proserpinaca palustris (Mermaid 

 Weed) which were grown in air, although habitually they are 

 aquatic. The difference in internal structure of leaves grown in 

 bright sunlight and in shade was also demonstrated. 



The question as to whether or not living plants absorb 

 moisture otherwise than by their roots gave rise to some dis- 

 cussion on account of a divergence of views held by the different 

 members of the Club. The discussion will probably be resumed 

 at some future date when more experimental evidence will be 

 presented. The value of dew to growing plants and the effect on 

 transpiration of relative humidity of atmosphere were also dis- 

 cussed at some length. The view presented by the leader that 

 excepting in the case of a few epiphytic plants which have 

 specialized organs for the absorption of water, dew is only in- 

 directly beneficial to plants i.e. in so far as it depresses trans- 

 piration, was challenged and rather discredited. 



It was also pointed out that the main causes of internal 

 modification of plant tisssues were variations in the intensity of 

 light and heat and also in available water supply. Of these 

 three important ecological factors the last mentioned was con- 

 sidered most important, although a few of the members held the 

 view that variations in heat are of even greater importance in 

 modifying plant structures. The main characteristics of three 

 great classes of plants were pointed out and discussed, viz.: 

 Mesophytes, or the normal plants of a locality not given to 

 extremes or excesses; Hydrophytes, or those plants that are 

 surrounded by excess of moisture and have to provide against 

 "drowning" by the development of an abundance of aeration 

 tissue; Xerophytes, which endure great privation from lack of 

 moisture and excess of heat, and which therefore must adapt 

 themselves to such conditions by developing an abundance of 

 cells for storing up water, by throwing out protective coverings 

 and by lessening transpiration through sunken and ]-irotected 

 stomata. 



Several miscellaneous slides were also exhibited illustrating 

 Halophytes (plants belonging to saline or alkah lands), Isophytes 

 (plants whose leaves are the same on both sides)^, Carnivorous 

 and parasitic plants. J- '^^ ^- 



