SCIENCE-GOSSIP. 



6i 



VARIATIONS OF THE LEAF-BLADE. 



By H. E. Griset. 



XTOTWITIISTANDING the numerous forces 

 ■'■^ that concur in the modification of the pecu- 

 liar external form of plants, a constant type is 

 maintained for the same species so long as they 

 exist under the sameconditions. Let these conditions 

 be changed and minute differences will be observed 

 in the colour, size or form of the leaves, flowers, 

 and other organs, which, if long continued, become 

 more marked and finally give origin to those 

 natural sub-species and varieties which seem to 

 connect one species with another. In this article 

 it is my intention to show some of the variations to 

 which the leaf-blade is subject in relation to the 

 above and other forces. The leaf-blades of many 



blade is usually broadly cordiform (fig. 6) ; it is 

 not unusual to find plants in shady places with all 

 the leaves narrow hastate, with large rounded 

 basal lobes divergent from the mid-rib at an angle 

 of 120° (fig. 7). 



Some plants of Ranunculus aquatilis have all the 

 leaves multifid, while others, especially in deep 

 pools, have palmately lobed or partite floating 

 leaves (sub-sp. heterophyllus). The lowest leaves are 

 always the most multifid. 



The leaves of Leontodon taraxacum are rather 

 variable as to their division, sometimes being very 

 undulated or lacinate and dentate ; while at other 

 times plants may be seen in which the lobes of the 



Fig. I, large leaf of CratiEgus oxyacantha ; fig. 2, typical leaf of Solatium dulcamara ; figs. 3-4, excessive 

 variations of leaves of S. dulcamara. All two-thirds nat. size. 



climbing and twining plants are very prone to 

 great modification, such as the leaves of the barren 

 stems of the common ivy, which are produced of 

 such different shape by cultivation. 



The common form of the lamina of Solayuim dulca- 

 mara, is three-partite, the large terminal lobe being 

 ovate, with a pair of divergent basal ones, (fig. 2) ; 

 in dry places they may sometimes be found quite 

 entire (fig. 3), and then closely analogous to the 

 leaves of Atropa belladonna ; and in damp and shady 

 woods they are five-partite, or even seven-partite, as 

 the one drawn here (fig. 4), found by the writer in a 

 dark pine-wood in Kent ; they consequently resemble 

 the pinnate leaves of solanaceous plants like the 

 tomato ; the terminal lobe may vary from broadly 

 ovate to narrow lanceolate. 



In the black bryony, Tamus communis, the leaf- 



upper part are pretty regular and almost sinuate 

 (fig. 5). A large leaf of this species I found measured 

 twenty-nine inches in length ; it was proportionally 

 narrower than the common type of the leaf. These 

 examples seem to point out that excessive dampness 

 favours the sub-division (or hinders the formation 

 of the parenchyma ? ) of the leaf-blade, which is 

 well illustrated in Ranunculus aquatilis. 



A solitary plant of Mercurialis percnnis, growing 

 among many others of the same species, had 

 narrow lanceolate leaves (fig. 8). 



As to size, the leaves of many plants differ 

 greatly, according to the position they occupy on 

 stem ; those nearest the root, being largest and 

 most divided, are the first to appear in spring, as is 

 well seen in many poplars and the horse-chestnuts. 

 A leaf of Quercus rohuv was 85 inches long, and 3 25 



