364 



SCIENCE-GOSSIP. 



SUCCULENTS AT KEW. 



By E. H. Wilson. 



(Continued from page 331.) 



If we consider the Euphorbiacae, we shall find 

 exactly parallel modifications. In Euphorbia fulgens 

 we have a thin stem with well-developed, persistent 

 leaves ; in E. splendens, succulent stems and par- 

 tially persistent leaves. E. tirucalli has a stout 

 trunk, with whip-like branches, while in E. abys- 

 sinica and others we find thick, columnar stems, 

 comparable with the cacti already mentioned. 

 In all of them, leaves are developed, but they are 

 merely transient. Most of the species have 

 spines, but they are usually short. In E. splendens 

 and E. bojerii, the stems are terribly spinescent, 

 and the spines I of E. gravdicornis make one 

 Bhudder to behold. Apart from the protection 

 afforded by the spines, these plants provide an 

 additional and perhaps even more effectual pro- 

 tection in the milky juice or latex they secrete 

 the properties of which are both acrid and vesica- 

 tory. 



To show that similar modifications occur in 

 monocotyledons, let us take the Liliaceae, as 

 represented at Kew Gardens. Dasylirion glaucum 

 has a rather slender trunk, clothed with the per- 

 sistent leaves and leaf -bases. The individual 

 leaves are sessile, almost linear, toothed, with an 

 excessively thick cuticle on both surfaces. D. 

 hookeri shows a huge, short, irregularly globular 

 trunk, surmounted by a few glaucous, sedge-like 

 leaves. In the genus Aloe the leaves are thick 

 and succident, with a central water-containing 

 tissue. Some species are deciduoris (A. cooperi). 

 Gasteria has similar succulent leaves, with a tough, 

 warty epidermis, the leaves being arranged in two 

 or three orthantichies. In Haworthia we have 

 short, succulent leaves forming rosettes, one sec- 

 tion with a thin, another with a thick, cuticularised 

 and warty epidermis. A similar state of things 

 obtains in Apicra, where the stem elongates some- 

 what, and the leaves are further reduced. An 

 interesting biological fact about these four genera 

 is that they will all hybridize. In Bulbine taules- 

 cens the leaves are almost subulate and fleshy ; in 

 Asparagus the leaves are reduced to minute scales, 

 flattened branches performing their frinction. 

 Finally, Bowcia volubilis goes a step further, as it 

 forms a bulb, but many years elapse between the 

 successive formations of normal leaves, which, 

 when formed, only last for a brief period. The 

 permanent assimilatory organs are here the 

 slender, much-branched inflorescences which 

 develop annually, and are for the most part 

 barren. 



What is perhaps even more remarkable, we can 

 trace all these grades of leaf-reduction in a single 



genus of the Compositae, viz., Senecio. The ex- 

 tremes of vegetative structure are probably 

 greater in this genus than in any other single 

 genus in the vegetable kingdom. Senecio subscan- 

 dens is a scrambling, semi-herbaceous species with 

 well-developed, pinnatisect leaves. 8. macroglossus 

 is a true climber, with thin, terete, twining stems, 

 and slightly succulent, ivy-like leaves ; S. articu- 

 latus has glaucous succulent articulated stems 

 bearing thin and glaucous sinuate leaves ; S. 

 pyramidatus is a semi-succulent, much-branched 

 species with almost acicular leaves ; finally, in S. 

 junceus, no leaves are developed, the stems being 

 green, terete, and ribbed, looking very like 

 Equisetum hyemale. 



A retrospective glance at what has been said, 

 points out very clearly the following interesting 

 fact ; that groups of plants widely separated by 

 botanical affinity and geographical area have, 

 under similar climatic conditions, followed parallel 

 lines of adaptation. So closely, indeed, do some 

 simulate others, that they become indistinguish- 

 able so far as external vegetative morphology is 

 concerned. For instance, remark the close resem- 

 blance between Cereus peruviana and Euphorbia 

 abyssinica, the former belonging to the Cactaceae, 

 the latter to the Euphorbiaceae. Again, who but 

 an expert could distinguish between E. aphylla 

 and Rhipsalis fusialis, or indeed, between any of 

 the following pairs of plants : Euphorbia pendula 

 (Euphorbiaceae) and Sarcostemma Australis (Ascle- 

 piadeae) ; Senecio junceus (Compositae) and 

 Sarcostemma viminale (Asclepiadeae) ; Rhipsalis 

 paradoxa (Cactaceae), and fitis quadrangularis 

 (Ampelidaceae) ; or finally Crassula lycapodiades 

 (Crassulaceae), and Lycopodium clavatum ? 



In many of these xerophytic plants, the basal 

 portion of the stem becomes enlarged, ultimately 

 forming a huge, more or less globular, structure 

 in which water and reserve food may be stored for 

 a very lengthy period. By aid of this, they can 

 withstand the longest period of drought. These 

 structures appear indiscriminately in groups of 

 plants widely remote from each other by descent, 

 as the following examples will prove : Testudinaria 

 elephantipes (Dioscoreae), Gerardanthus tomentosus 

 (Cucuibitaceae), Fockia glabrata (Asclepiadeae), 

 Stephania rotunda (Menispermeae), Beaucarnea 

 recuivata (Liliaceae), etc. 



Another interesting fact concerning xerophytes 

 generally, is their ready means of vegetative pro- 

 pagation. In almost all of them, any part of the 

 regetative structure will give origin to young 

 plants under suitable conditions. The jointed 



