Burns. — Heterophylly in Proserpinctca palustris, L. 581 
a disturbance is certainly made in the case of cuttings — may cause the same 
reaction in the plant named. 
While engaged in an ecological study of certain parts of the Huron 
Valley, in the vicinity of Ann Arbor, my attention was repeatedly called 
to the great variations in the form of the leaves of the plants growing in 
the margins of the river, and especially to those of Proserpinaca palustris , 
Ranunculus multifidus , and Ranunculus aquatilis. The last two are familiar 
through the work of Goebel and others. Proserpinaca was first described 
by McCallum, who gives us a very satisfactory account of this plant, 
illustrated with some good photographs and drawings. 
Proserpinaca palustris grows in great abundance in the vicinity of 
Ann Arbor, usually in water about 30 cm. deep. It may, however, 
grow in water one metre deep. At Dead Lake it grows in great abundance 
near the shore, and some plants are out of water during a large part of the 
summer. It is very easy of culture both on land and in water. The 
‘land-type’ of leaf is lanceolate, from 3 to 5 cm. in length and 6 to 
8 mm. broad. The margins are serrated (PL XXXVIII, Figs. 1 and 5). 
The ‘ water-type 9 of leaf is very different. It is finely divided, with a central 
rib and from three to five filamentous divisions on each side (Figs. 1 and 4). 
These divisions are almost round in cross-section. 
A comparison of the development of the two types of leaves shows 
that they are exactly alike in form in the primordium, and that they con- 
tinue to develop along the same lines for a comparatively long time, 
independent of external conditions. Thus, whatever factor or factors 
determine the type of leaf to be developed from a given primordium must 
come into play relatively late. Each type of leaf begins as a small pro- 
tuberance on the side of the vegetation-point. Lobes soon appear on the 
margins in basipetal order. The leaf and each of the lobes ends in 
a peculiar gland-like structure which very soon reaches its full development. 
Thus far all leaves have the same history of development (Fig. 6). The 
final type of leaf formed depends upon the later growth of this primordium. 
If the growth is confined to the central portion, a broad leaf with serrated 
margins is the result (Fig. 5). On the other hand, if the growth is 
confined mostly to the ribs, a finely dissected leaf is produced (Fig. 4). 
Development of the Seedling. 
A large number of the seeds were gathered in October and divided 
into four lots of twenty seeds each. Those in lot ‘ a ’ were placed in a damp 
chamber between filter paper ; those in lot c b ’ were placed in soil under 
eight inches of water ; those in lot ‘ c ’ were placed in two-inch pots ; those 
in lot ‘ d ’ were planted in two-inch pots and then placed in a pail of water. 
The first three were left in the greenhouse under good conditions for 
