xi] THE WATER BUTTERCUPS 145 



to a certain point they develop alike and are both deeply sub- 

 divided ; then the water leaf ceases to change in shape and the 

 segments merely increase in size, while the floating leaf gradu- 

 ally assumes its typical, relatively entire form. In general, the 

 type of leaf produced by the plant can be changed at will by 

 altering the conditions. If a plant that has begun to grow on dry 

 land, be submerged, the new leaves produced by further growth 

 are of the submerged type. The existing leaves, though they 

 cannot alter their form, may, in the basal region which is still 

 capable of growth, develop transitional features as regards the 

 epidermis. 



Among species related to Ranunculus heterophyllus. Fries, 

 in which floating as well as 

 submerged leaves are usually 

 present, we find some, such as 

 R. fluitans^ Lamk., in which the 

 floating leaves are rare, while in 

 R. circinatuS) Sibth. they are un- 

 known. On the other hand, R. 

 hederaceus, L. (Fig. 93), which 

 generally grows in shallow ponds 

 and ditches, possesses lobed reni- 

 form leaves only, and none that 

 are finely divided and belong to 

 the submerged type. 



Heterophylly is not confined 

 to the Batrachian Ranunculi, 

 but is widespread in the genus. 

 Ranunculus Flammula, the Lesser 

 Spearwort, though generally 

 terrestrial, may live as a water 

 plant 1 , in which case it can develop both submerged and floating 

 leaves. The submerged leaves are not, however, subdivided as 

 in the case of Ranunculus heterophyllus. Heterophylly has also 



1 Bailey, C. (i 8 87), West, G. (1910), Gluck,H. (191 1); references will 

 be found in West, G. (1910) to the earlier writers who observed this form. 



FIG. 93. Ranunculus hederaceus, L. 

 An example of a Batrachian Ranun- 

 culus with undivided leaves, (f nat. 

 size.) Shallow pool, Ware Undercliff, 

 March 27, 1912. The gynaeceum, G, 

 is bending down to ripen under water. 

 [A. A.] 



A. W. P. 



