Observations upon some Noteworthy Leaf Variations. 295 



shade, since it has been found that in a plant growing in re- 

 lative shade, the leaves were reduced to less than one-third 

 the average, normal size. On the other hand, strongly 

 vegetative shoots were found to bear leaves which were not 

 only conspicuous for their alteration of form, but notable for 

 being 2^ times larger than the normal and eight times larger 

 than the reduced leaves of the same plant growing under the 

 same general conditions of illumination. But here again we 

 have an exception to the usual law of development, since 

 these leaves were directly exposed, and their entire course of 

 development was under the influence of sunlight which served 

 in no way to inhibit their growth. It is clear then, that we 

 cannot find an adequate explanation for such variations, either 

 in diversion or energy incident to the reproductive period, or 

 in the adaptation of the leaf to conditions of illumination of 

 which they seen to have been wholly independent. It will be 

 recalled that these shrubs were top pruned in the spring of 

 1093. During the following summer they made but moder- 

 ate growth which was chiefly manifested in the development 

 of numerous, wiry side branches. The plants therefore en- 

 joyed a period of comparative rest, during which there was no 

 doubt a considerable accumulation or energy in the form of 

 reserve food stored within the tissues. The somewhat more 

 than usually favorable conditions for growth, prevalent during 

 the past summer, formed a very happy combination of circum- 

 stances and permitted a liberation of the accumulated energy 

 as expressed in shoots of remarkable size, and foliage of unus- 

 ual form and dimensions. The abnormally large leaves, 

 therefore, may be held to be the expression of unusually 

 vigorous vegetation independently of conditions of light and 

 shade ; while the reduced leaves constitute an expression of 

 diminished vigor as first manifested in the weakly branches. 

 This explanation therefore finds justification in certain facts of 

 much significance. (1) The reduced leaves are invariably 

 produced upon small wiry branches indicative of poor nutri- 

 tion ■ (2) the most vigorous shoots arise from pruned 

 branches, often close to the point of excision where there 

 would be likely to be an unusual deposit of food materials ; 



