lyS BIOLOGICAL LECTURES. 



tiated as fertile ones, for the general plan of structure of the 

 sterile and fertile leaves is very much the same, especially in a 

 very early stage of their development. The different degrees 

 of fixation of the reproductive characters on these very young 

 fertile leaves, at the time when the plant is suddenly deprived 

 of the fully developed vegetative leaves, determines to a great 

 extent the individual character of the transformed structure 

 which assumes the responsibility for the entire labor of the leaf 

 system heretofore definitely divided between different individual 

 leaves or structures. This individual character is also influ- 

 enced to a certain extent by the readiness with which the indi- 

 vidual plant puts forth new vegetative leaves. So with the 

 various combinations of these two conditions there results the 

 very wide variation which is here presented in the forms of 

 the transformed fertile leaves, showing almost every conceivable 

 gradation which we could naturally expect when we take into 

 consideration the course of development of the ordinary leaves. 

 The extremes of these variations present very doubtful cases. 

 On the one hand, there are fertile leaves which have felt the 

 slightest touch of this influence controlling the transformation, 

 and it is extremely diflicult to say whether it is entirely normal 

 or not. On the other hand, there are cases where the greatest 

 demand has been made upon a leaf of the fertile kind at so 

 early a period in its development that it becomes to all intents 

 and purposes a vegetative leaf, and possesses so little of the 

 individuality of the fertile leaf that we cannot, in our ignorance, 

 discriminate it from a leaf of the vegetative kind. 



The plan this season, though not carefully originated, was to 

 extend the experiments to phanerogamous plants in order to see, 

 especially, if the pistils, which are supposed to be homologous 

 sporophyllary organs, could be forced to take on the form and 

 function of the vegetative leaves by cutting off the latter. This 

 part of the experiment, I say, was not well originated, since, 

 on account of numerous other duties, no selection of plants 

 was made until operations were begun in the spring. For this 

 reason some of the plants operated on were too far advanced, 

 while others were ill chosen, because the sporophylls appeared 

 at the same time as the vegetative leaves. This latter difficulty 



