34 The Ottawa Naturalist. [May 



variation. "Within recent years", continued the speaker, "a 

 new light has been thrown on this question by the appearance 

 of the theories of Mendel, DeVries and Johannsen. The basic 

 principle of these theories is that an individual plant or 

 animal is composed of distinct units which correspond in a sense 

 to atoms in chemistry. By crossing two individuals a combin- 

 ation of units takes place which finds expression in a new form 

 combining the characters of the two. 



If the above theory of "Unit characters" is correct heredit- 

 ary variation must take place in either of two ways, viz. 



(a) Through new combinations of characters by crossing, or 



(b) By the sudden alteration in the unit constitution of the 

 individual itself, a phenomenon to which the name "Mutation" 

 has been applied. 



This idea is clearly inimical to the old Darwinian belief in 

 the omnipresence of hereditary variation at least in so far as it 

 concerns those plants which naturally self-fertilize. 



If we accept the idea that the various forms within an old 

 race arise either as the result of natural crossing or by mutation, 

 our next problem is to determine, if possible, how often these 

 combinations and mutations take place, and which is of the more 

 frequent occurrence. 



DeVries, the real founder of the mutation theory, has classi- 

 fied mutations under two catagories, viz., Retrogressive Mutation 

 and Progressive Mutation. The first owes its existence to the 

 dropping out of a unit while the latter has arisen, according to 

 DeVries, through the acquisition of a new unit. Despite all that 

 has been said and written about the mutations theory and its 

 great practical importance, the speaker had not found it very 

 seriously considered in Europe. While there were evidences to 

 show that so-called retrogressive mutations probably occur 

 occasionally, yet he had not been able to find an unquestionable 

 example of a progressive mutation. On the other hand the 

 whole manner of thinking in the most progressive centres, such 

 as Cambridge, England, (Bateson, Punnet, Wood, etc.), Copen- 

 hagen (Johannsen, Ravn, etc.), Berlin (Bauer), Austria (Tscher- 

 mak), Sweden (Ehle and Tedin), and many other places was after 

 the combinations idea. This idea has developed enormously 

 during the past ten years following the extensive work which has 

 been done in artificial cross fertilization, a work which provides 

 a means of studying the unit constitution of the individual plant 

 or animal and thus of throwing new light upon the great problems 

 of heredity. 



It has long been held by certain authorities that natural 

 cross-fertilization among such supposedly self-fertilizing plants 

 as wheat, oats, barley and peas was practically impossible. Re- 



