154 Rhodora [JuLy 
the Sagittarias possessed no more highly differentiated leaf than the 
present ribbon-form leaf of the seedling? 
It is easier to answer the question with reference to the spoon- 
shaped intermediate leaf (7). In the old-age of the plant — that is, 
of any particular shoot of the branching rhizome in the species repre- 
sented — the leaves retrace the course of development as the vegetative 
vigor becomes exhausted and second childhood comes on. ‘The series 
fg, Fig. 7, is a reversionary series, beginning with hastate forms 
more and more unlike the sagittate character leaf, and ending with 
very narrow-bladed lanceolate forms. These latter stand well out of 
water, so that the direct action of that medium is eliminated from the 
case, and even were there no other Sagittarias and the Alismas, we might 
be tolerably sure,— from the doué/e appearance, in youth and in old age, 
— that the lanceolate form represents a return to what was once the 
farthest limit of differentiation. 
'The nature of the linear, grass-shaped early leaves of the seedlings 
and new shoots, which seem to be the same thing as the ultimate leaves 
of several species, is perhaps doubtful. They are spoken of by several 
writers as ?Ay/Z/odia. If the term has any distinctive meaning, it im- 
plies reduction from a bladed to a bladeless condition. The linear 
leaves are looked upon as petioles, with the notion that a part normally 
produced in addition to and beyond these bodies is suppressed through 
the influence of the surroundings. 
Seedling stages should throw light on the question. Sagittaria 
Montevidensis, of South America, passes through its seedling stages 
very slowly, and presents a very complete series of transitional forms. 
In these there is every indication that the lanceolate or elliptical blade 
(4 ) is derived from the linear forms not by addition at the tip, but by 
gradual differentiation of the terminal region of the linear leaf to form 
the ultimate blade, while the lower part of the original body (or blade) 
becomes gradually thickened and then rounded to make the ultimate. 
petiole. If this is so, the grass-shaped early leaves are not reduced 
forms in the sense appertaining to the phy//odia of the Acacias. "They 
are in fact probably not 2AyZe«ia; they seem to be early complete 
forms giving rise by progressive and structurally necessary steps to the 
adult differentiated leaf. 
The linear leaves of the seedling, forming in this manner the basis 
of an evolution toward the full character leaf, seem little like cases of 
what the zoologists would call larval adaptation. It is probably not 
