Variation occurring in Biscutella laevigata. 



15 



III. Surface glabrous. — This class includes — 



(a) Leaves in which the whole upper surface is glabrous, 



except, perhaps, for one or two hairs which, as it were, 

 overflow from the continuously hairy margins at the 

 level of the leaf-teeth. 



(b) Leaves in which both surfaces are glabrous, and, further, 



the marginal hairs are being confined to certain 

 definite points — the leaf -teeth. 



(c) Leaves in which the lamina is wholly destitute of hairs. 



[In types II and Ilia the under surface of the leaf was not 

 examined, and the scattered hairs occasionally occurring on the 

 midrib were also disregarded.] 

 Types I and II are so well marked that it is rare to find a leaf full 

 grown, and with hairs on the surface, which cannot be referred with 

 confidence to either category. 



The flowering stem is hairy for a longer or shorter distance from 

 the base in plants belonging to type I ; whereas in those belonging to 

 types II and III it is usually glabrous. 



Details of Experiments. 



Ripe seeds collected from plants growing in the Yal Formazza 

 were divided into three sets, which were sown respectively in August, 

 1895, and in February and March, 1896 ; in addition to this material 

 a few plants which survived transplantation from Italy, together 

 with some specimens in the Cambridge Botanical Garden (which 

 had been raised from seed supplied by M. Correvon, of Geneva), were 

 also placed at my disposal. The seedlings were raised in pots under 

 glass, and either planted out in the open in the spring, or repotted 

 singly for greater convenience of manipulation. A careful examina- 

 tion of each leaf of the young plants brought to light a fact of con- 

 siderable interest ; it was noticed that in certain cases the first-formed 

 leaves exactly resembled one another as regards the nature of the 

 leaf surface, whereas in others the successive leaves exhibited degrees 

 of hairiness varying more and more widely from the original type. 

 In order to obtain a record of each leaf, it was found necessary to 

 take special precautions to protect the plants as far as possible from 

 the attacks of slugs and snails, to whom the leaves of this species 

 seem to be especially palatable. The pots were therefore placed upon 

 cinders, or surrounded with soot ; if not thus protected many of the 

 younger leaves would in a single night be reduced to bare midribs, or 

 in the case of seedlings, the stump of the stem was often all that re- 

 mained. The plants with smooth-surfaced leaves were more liable to 

 attack than those that were hairy, although the latter did not wholly 

 escape. In one batch of seedlings, which were all placed under the same 



