1900] Leavitt, — Reversions in Berberis and Sagittaria 151 
embryonic and post-embryonic stages have been attended to, but the 
former by far the most thoroughly in both Zoology and Botany. 
In Botany investigations of the young stages subsequent to the 
formation of the embryo, in order to discover hints of relationship 
that must disappear at a little later date in the life history, have been 
relatively few. But several workers are now paying attention to the 
matter, with good results. Some of the most interesting discoveries 
are coming from investigations of the minute anatomy of seedlings. 
It scarcely need be said that the subject of reversions is of great 
importance in the study of the processes of heredity ; and that in some 
respects plants make better subjects than animals in inquiries concern- 
ing the laws of reversion. Leaf-forms, in general simple, but in enough 
cases not simple to excess, are fit subjects for such inquiries. 
BERBERIS. In Figure 1 of the accompanying plate I have repre- 
sented a two-months’ seedling of Berberis vulgaris. Were the young 
plant found growing wild, and at a distance from mature plants of the 
species, its parentage might not be suspected, the leaves are so unlike 
those of the adult condition in respect to the length of the petiole and 
the shape of the blade. The blade of the latter, or full leaf, is broader 
toward the apex and tapers very gradually to its junction with the 
extremely shortened petiole. ‘The youthful lamina reverses this, being 
narrower above and more or less cordate at the base. It is distinctly 
jointed to the well-developed petiole, the earlier and later leaves thus 
agreeing in being unifoliolate. 
Bushes of this species, four years old, from which I collected leaves 
last fall, still showed the leaf-character of the seedling in preponderance 
over shorter-petioled forms approaching the adult type. And, on iso- 
lated branches of old bushes, I have this spring found persistent petioles 
much longer than the normal, the stalks, without much doubt, of 
similar reversionary leaves. For I look upon the “ abnormal” forms 
as good examples of reversion. 
We might guess that we have here the reappearance of an ancient 
type from its constant occurrence at the period of life when both plants 
and animals manifest ancestral traits. A like trait in the seedling of 
an allied species, Berderis Thunbergit (Fig. 3), makes the inference of 
a reversion still more plausible. 
Of course the final and irrefutable evidence of reversion is the 
direct comparison of the form in question with an ancestral type pre- 
served in the rocks. But ancestral types are preserved also in living 
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