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ECO LOG Y. 



sterile leaves from quite a large patch of the sensitive fern, once 

 in May, and again in June. In July, when the fertile leaves 

 were appearing above the ground, many of them were changed 

 partly or completely into sterile leaves. In all some thirty plants 



Fig. 448. 

 Normal and transformed sporophyll of sensitive fern. 



showed these transformations, so that every conceivable gradation 

 was obtained between the two kinds of leaves. 



627. It is quite interesting to note the form of these changed 

 leaves carefully, to see how this change has affected the pinnje 

 and the sporangia. We note that the tip of the leaf as well as 

 the tips of all the pinrue are more expanded than the basal por- 



