No. 626] SHORTER ARTICLES AND DISCUSSION 277 



describes the occurrence of subdivided leaves of the water tj-pe 

 on lateral shoots of normal land plants of Limnophila hetero- 

 phylla. A corresponding reversion has been observed in the case 

 of the side branches of plants of Proserpinaca paliistris develop- 

 ing in the air from a plant whose main stem was producing the 

 mature type of leaf; by removing the growing apex of the stem 

 in June, side branches of the "water tj-pe" were induced to de- 



The interest of these lateral shoots, which show a reversion to 

 an ontogenetically earlier type of leaf, is enhanced by the fact 

 that C. and F. Darwin in "The Power of Movement in Plants" 

 have recorded a case of the occurrence, on lateral shoots, of leaves 

 whose characters are probably phylogenetically earlier than those 

 which the species normally exhibits. Their observations related 

 to the sleep habits of the allied genera, Melilotiis and Tri folium. 

 They noticed in Melilotus Taurica that leaves arising from young 

 shoots, produced on plants which had been cut down and kept in 

 pots during the winter in a greenhouse, slept like those of Tri- 

 folium, with the central leaflet simply bent upwards, while the 

 leaves on the fully grown branches of the same plant afterwards 

 slept according to the normal Melilotus method, in which the ter- 

 minal leaflet rotates at night so as to present oue lateral edge to 

 the zenith. They suggest that Melilotus may be descended from a 

 form which slept like Trifolium. 



The idea that the "juvenile" leaves produced on lateral shoots 

 may in some eases represent an ancestral type, is consistent with 

 the facts in the case, for instance, of the Alismaeese, provided that 

 the ' * phyllode theory ' ' of the monocotyledonous leaf be accepted 

 in the sense advocated by Professor Henslow and the present 

 writer. According to this theory, the ancestral leaf of this family 

 was ribbon-shaped, while the oval or sagittate blade (or "pseudo- 

 lamina") represents a later development — a mere expansion of 

 the apex of the petiole. The submerged youth leaves of this fam- 

 ily would thus represent a reversion to phylogenetically older 



If the interpretation of heterophylly indicated in the present 

 paper holds good at all widely, the teleologieal view of the sub- 

 merged leaf must be considerably uiodifiod. Tlie present writer 

 would like to suggest that, for tlif (.Id conr.'pridii of heterophylly 

 asinducedhy aquatic life, we sliciuld substitute the idea that such 

 a difference between the juvenile and mature fi)nns of leaf as 

 would render the juvenile leaf well -uited to aifuatie life, has been 



