1912] The Ottawa Naturalist. 27 



Unfortunately, the term "variation" has been applied to 

 a great number of phenomena of a very different nature, and 

 in the mind of most people is something that can not be clearly 

 defined. As a result, the biological and practical significance of 

 variation is not clearly appreciated. 



1. The individual plants of a species sometimes present such 

 striking differences at different stages of development that the 

 observer might readily regard them as different species or even 

 different genera, where, as a matter of fact, only different ages 

 are represented. Thus, a great number of species of the genus 

 Acacia present a delicate fern-like foliage when young, whereas 

 the old plants are clothed with narrow and simple leatherv 

 organs, which in shape and texture resemble the leaves of the 

 mistletoe. Conifers, such as Thuja and Juniperus, which when 

 fully developed have flat, scale-like leaves, are when seedlings 

 provided with typical needle-leaves. Such juvenile forms can 

 be fixed by cuttings and they then keep their peculiar needle- 

 leaves for many years, presenting small trees, which are no more 

 like the Thuja or Juniperus than a spruce is like a pine tree. 

 Such fixed, juvenile forms have been described as species of a 

 special genus, Retinospora. 



2 . Light sometimes causes variations of the most astonish- 

 ing nature. The well-known blue bell, Campanula rotundifolia, 

 generally has only long, narrow leaves. When the plants are 

 growing in grass, however, or when they are young, basal 

 leaves occur, which are round or kidney-shaped. Whether or 

 not a plant shall have the latter kind of leaves is a matter of 

 light, as can be demonstrated by the following experiment: 

 enclose the upper part of a blue bell plant in a box of wood, 

 and the new shoots developed from the enclosed parts of the 

 plant will carry leaves round or kidney-shaped and in all respects 

 similar to the round or kidney-shaped root -leaves. 



3. Amphibious plants often present one water-form and 

 one land-form, which are widely different from each other. 

 Numerous experiments have shown that the water-form can be 

 changed into the land-form and vice versa, and that the same 

 individual can present shoots of both types at the same time. 

 Such variation, induced by the amount of water available, can 

 be observed in such plants as water parsnip (Sium), water 

 plantain (Alisma Plantago), knot -weed (Polygonum amphibium), 

 numerous species of Ranunculus, etc. 



4. Other plants, when placed in certain environments, 

 often show striking variations. Thus, it is rather common for 

 plants growing in a climate where hot winds prevail, such as in 



