66o 



LECTURE XXXVIII. 



{Nepenthes), where, however, the ' pitcher' already described (Fig. 247, p. 379) only 

 arises at the tip of the tendril after the latter has wound itself round a support. 

 In many Bignonias, Cobcea scandens, the common Pea, and its allies the Vetches, &c., 

 the anterior portion of the pinnate leaf becomes transformed into very thin, filiform, 

 and (in the first-mentioned plants) much- branched tendrils ; and in Lathyrtis aphaca 

 indeed the whole leaf is replaced by a tendril. 



These tendril-plants, of which Hugo von Mohl (1827) already knew 465 species, 

 but the number of which is certainly far larger, occur for the most part among 

 Monocotyledons and Dicotyledons, although several Cryptogams are possessed of 

 similar organs. They are met with, however, in most abundance among the Dicotyle- 

 dons, where in fact the distribution of physiological labour in general attains the 

 highest development. The formation of tendrils is, as a rule, by no means to be found 

 in all the members of a group in which it occurs. In the Cucurbitaceae, Ampelidese (the 



Vine and its allies), and the Passiflorse this is of 

 course the case ; but elsewhere it is usually only 

 individual genera of a family, or individual species 

 of a genus, which form tendrils. And this, 

 moreover, is true of all climbing plants. Among 

 the allies of the Ivy, it is this plant only 

 which climbs in its peculiar way, and that the 

 same is the case with twining plants is shown 

 by the very close relationship between the Hop 

 and the Hemp — the former being a typical 

 twining plant, the latter a stiffj upright, and any- 

 thing but a climbing species. Just as in the case 

 of the climbing species, also, the other physio- 

 logical properties are independent of the sys- 

 tematic relationship; in the genus Ranunculus, 

 for example, we find submerged or floating 

 aquatic plants, as well as marsh and terrestrial plants; among the Orchidese 

 ordinary land-plants with or without chlorophyll, and in the tropics epiphytes 

 living on trees, and the aerial roots of which serve as organs of attachment. 

 These may suffice to show the reader by the way how independent the systematic 

 or phylogenetic relationship of the physiological adaptations may be, and con- 

 versely. We may now return to the exclusively physiological consideration of the 

 tendril-plants. 



^ The distinctive properties of tendrils are the more pronounced the more ex- 

 clusively they serve the one purpose of organs of attachment for climbing, and 

 therefore the less they partake of the nature of leaves or parts of stems in other 

 respects— in a word, the more completely the metamorphosis is accomplished. 

 Among these are especially to be noticed the simple or branched filiform tendrils 

 of the Cucurbitaceae, Ampelidese and Passiflorse. One of these typically developed 

 tendrils is shown at Fig. 375 a in the mature state, after it has embraced a support 

 with its apical part and then become rolled up. What is here stated applies 

 particularly to such true tendrils. 



The characteristic properties of tendrils become developed when they have com- 



FIG. ^j6.— Tropaolietn viinits. The lonff petiole 

 a aa of the leaf / is sensitive to continued contact, 

 and has coiled itself round the support and round its 

 own stem si so that the latter is fixed firmly to the 

 former, a is the axillary bud of the leaf. 



