SCIENCE-GOSSIP. 



117 



LEAF VARIATION. 

 By J. A. Wheldon. 



TN the August number of Science-Gossip, Mr. 

 H. E. Griset, in an interesting and suggestive 

 article, calls attention to the variation in the shape 

 of the leaf lamina of plants. It is probable that 

 the writer's deduction, that "excessive dampness 

 favours the sub-division (or hinders the formation 

 of the parenchyma) of the leaf- blade," may be 

 correct in the case of Ranunculus aqiiatilis, and other 



several species of Potamogeton. In some of the 

 above, the leaf is reduced to the modified petiole 

 only. 



Thus far I agree with Mr. Griset ; but I do not 

 find in my experience that mere dampness of soil or 

 atmosphere, as distinguished from total submersion, 

 tends to hinder the expansion of the parenchyma. 

 Indeed, I should imagine that such a moist en- 



Instances of Leaf Variation. 

 Figs. I, 2, 3 and 4, dandelion leaves; figs. 5 and 6, saw-wort leaves (all two-thirds natural size). 



plants which grow immersed in the water. In the 

 species above - mentioned, I have observed the 

 capillary leaves almost totally disappear, and only 

 leaves of the floating palmate or partite kind be 

 developed, when the water supply runs short in a 

 dry season. 



Many other partially submerged aquatic plants 

 exhibit diminution, or even total suppression, of 

 the parenchymatous portion of such leaves as grow 

 beneath the surface of the water, e.g., Hclosciudum 

 inundatum, QLnanthe phcUandiluin, CE. fluviatilis, 

 Callityiche, .ilisma vatans, Sagitturia sagittifolia, and 



vironment would rather encourage its expansion, 

 and thus theoretically would lead one to expect 

 that leaves growing under conditions of greatest 

 moisture would exhibit the least tenuity of division. 

 Take an example cited by the author of the article. 

 The various species or sub-species of Taraxacum 

 grow in a wide range of habitats. T. palustre, 

 which usually inhabits the dampest places, has 

 leaves exhibiting the greatest expansion of the 

 blade ; in the T. dcnslconis of the roadsides and 

 fields they are more deeply cut, and the maximum 

 amount of division is reached in T. erythrospermum, 



