Volume 14 Number 3 



The Plant World 



A Magazine of General Botany 

 MARCH, 1911 



THE INHERITANCE OF HABITAT EFFECTS BY PLANTS. 



D. T. MAC DOUGAL. 



It is unanimously agreed that organisms, plants as well as 

 animals, change individually in aspect, in form and structure of 

 organs, in functionation and habit as they encounter swamps, 

 saline areas, gravelly uplands or slopes, climatic differences 

 identifiable with latitude or elevation, and other physical and 

 biological factors. It is assumed that these somatic alterations 

 are accommodative and adaptive, making the organism more 

 suitable for the conditions which produce the changes. Such 

 an assumption is an over-reaching one, and it is by no means 

 to be supposed that the plant is a perfectly reacting automaton 

 capable of adjusting itself to every agency which it may en- 

 counter. 



Any analysis of the changes which an organism undergoes 

 after transportation to a new habitat will disclose one or a few 

 alterations which might be of advantage in dealing with the 

 newly encountered conditions, but with these there are many 

 others, direct, necessitous, atrophic, or hypertrophic as to organs, 

 which have no relation whatever to usefulness or fitness. Thus 

 nearly all broad-leaved plants from the moister regions mature 

 their leaves at smaller dimensions than the normal and this 

 might appear as a fairly direct accommodation. A microscopic 

 examination of these leaves will show that, in some instances 

 at least, the total number of stomata is equal to that of an 

 average leaf, so that the number on any given area is unusually 

 large. The change therefore, would be one reducing the 

 chlorophyll exposure but actually increasing the rate of trans- 

 piration for the reduced surface remaining. Similar "misfits" 



* Adapted by the author from Presidential .\ddress on "Organic Response" before the 

 Society of American Naturalists, Ithaca. Mew York, December 29, 1910. The original 

 text is to be found in the American Naturalist for January, 1911 



