Burns. — Hcterophylly in Proserpinaca palustris , L. 583 
on the bench in ordinary conditions. All three sets were kept in the green- 
house. During the entire winter all of these plants produced the ‘ water- 
form’ of leaf. None of them grew luxuriantly. The lobes on the leaves 
of the submerged plants were longer than those of the other two, but the 
type of leaf was the same. One fact observed was very interesting. The 
plants in the air did not grow erect, and those in the water seemed to grow 
aimlessly round, never projecting their vegetation-points above the surface, 
although the growth in length was more than sufficient. 
Early in the spring the plants behaved quite differently. Those in 
the water projected above its surface and produced entire leaves ; those 
not in water grew erect and they too produced the entire or £ land-type ’ 
of leaf (Fig. 2). In the late spring of the present year this change in 
behaviour took place about four weeks later than it did in the year previous, 
when we had an early spring. Had I been able to improve the vegetative 
conditions under which my plants were growing, I am confident the plants 
would have produced their entire leaves much earlier. 
Cuttings made early in May, from stems producing the ‘ water-type ’ 
of leaf in water, begin to produce the ‘ land-type ’ of leaf when grown in air 
much earlier than the control plants left in water. 
A number of cuttings were made from the water-form of Ranunculus 
aquatilis. These were rooted in sand and potted, the pots being out of 
water. They grew two years in the greenhouse, never growing erect, but 
forming a dense tuft on the earth in the flower-pot and rooting at every 
node. The water-form, on account of weakened illumination, stretches its 
internodes. None of the plants produced the three-cleft leaf 'opposite or 
in the immediate vicinity of the blossom.’ The same finely divided ‘ water- 
leaf’ was formed for two years in air, only differing from the leaf developed 
in water in the length of the lobes. None of my plants blossomed, but 
I found one plant growing in the air near the water’s edge, which was 
producing flowers. This plant produced only the * water-type ’ of leaf. 
A comparison of the cross-sections of lobes from leaves developed 
in water and those developed in air shows marked differences in 
anatomical structure. The leaf of the latter is dorsiventral. The epi- 
dermal system is well developed both in regard to the thickness of the 
cuticula and the absence of chlorophyll-bodies in the epidermal cells. 
The mesophyll is differentiated into palisade and spongy parenchyma. 
The fibro-vascular bundle contains from six to ten well- developed vessels. 
Stomata are present. The leaf of the water-form is finely divided into 
cylindrical lobes whose tissues are little differentiated. The cuticula is 
very thin, and the epidermal cells contain fully as much chlorophyll as 
any cell in the mesophyll. The cells of the mesophyll are not differentiated. 
There is a marked reduction in the number of vessels found in the bundles. 
Only a few stomata are found, and these were not fully developed. 
