147 

 Specific Problem: What is Meant by Variation? 



Variation is one of the numerous words which have a number 

 of different connotations. It should be clear at the start that the 

 looser, broader meanings are definitely excluded; that the word 

 is not used here in the common interpretation as referring to the 

 range of differences among a group of sibs, or between the in- 

 dividuals of a larger species population. The meaning can be 

 finally narrowed and sharply delimited to the desired applica- 

 iton, as indicated in the preceding paragraph, by raising the 

 question : Will evolution take place if offspring always repeat 

 the exact characteristics of their parents? In other words, why 

 must variation occur as a process in reproduction if new forms 

 are to occur? 



Is there any evidence of such variation? Is there any ma- 

 terial which can be introduced into the school laboratory to help 

 in answering the questions raised? In this connection, the 

 Boston fern series, a number of which are common in the florist 

 trade, furnish excellent material for class study. They are rela- 

 tively common, and the material is not difficult to obtain. The 

 range of variation between the different varieties is wide, the 

 differences well-marked, and the material is large enough so 

 that the differences can be easily discerned. The total number of 

 scores of types have had a recent history. The method of repro- 

 duction is entirely vegetative, thus eliminating any complicacion 

 of the possible influence through hybridization. Incidentally, it 

 may be noted that the Brooklyn Botanic Garden has served for 

 nearly twenty years as a source of sets of specimens of these 

 ferns, both series of leaves and of growing plants for experimen- 

 tal and teaching use. So far as material is available, the writer 

 will be glad to furnish further material of this sort. 



The mode by which variation must have taken place in these 

 fern types can be easily pointed out, and is illustrated in figure 1. 

 This shows a parent plant of the wild sword fern {Nephrolepis 

 exaltata) from which the Boston fern was derived, in association 

 with three offspring which have arisen along a lateral stolon. 

 Such stolons are common in florists' or house specimens of Bos- 

 ton fern varieties, and the method of vegetative propagation 

 along stolons can usually be demonstrated by digging up a little 

 surface dirt around a well-established pot plant, or a demonstra- 



