Observations upon some Noteworthy Leaf Variations. 297 



apply, for we there find the lowest member of the series (1) to 

 be the largest, and the others successively smaller. The same 

 law is fully applicable to Spiraea in which the modified leaves 

 always become simplified in form as well as reduced in size, 

 while in Lonicera they are reduced in size without any special 

 simplification. Now in accordance with our present views 

 respecting the evolution of leaves, such simplification of form 

 and such reduction in area, must be regarded as of the nature 

 of reversions to more primitive types, as is so well exemplified 

 in Nephrolepis, from which we may conclude that the Loni- 

 cera, which is chiefly distinguished by reduced foliage, is 

 essentially a primitive form of the plant, and the same may 

 also be said of the flowering branches of Spiraea. Such a 

 view would harmonize with our knowledge of the general 

 effects of defective nutrition, a view which otherwise gains 

 force from the fact that the most highly developed foliage of 

 Lonicera on shoots of unusual growth, is obviously the direct 

 product of exceptionally favorable conditions of which ample 

 nutrition must be regarded as one, if not the dominant factor. 

 In these facts, then, we have a means of determining at least 

 some of the developmental stages through which the leaves 

 must have passed. 



Instances will readily recur to one, of trees like the com- 

 mon basswood (Ti/ia americana), and the linden (Ti/ia 

 europea) in which there is such constancy in the character of 

 the foliage that, were the leaves to be found entirely apart 

 from the tree, it would nevertheless be possible to determine 

 the genus beyond all reasonable doubt, and even the species 

 might be ascertained with reasonable certainty. The same 

 would hold true of Hydrangea, Berberis, Catalpa, Syringa, 

 Philadelphus and many others. There would be consider- 

 able doubt, however, in such a case as that of Cekistrus 

 articulatus, while there would be positive uncertainty as be- 

 tween the leaves of the young plant and those of the mature 

 stem in Ampelopsis veitchii, the mature leaves of Spiraea 

 trilobata van houttei and much more in that of Lonicera tar- 

 iarica. In Ampelopsis veitchii and Spiraea van houttei it 

 would be quite possible in accordance with palaeontological 



