Dec. iT, 1 8 74 J 



NA TURE 



137 



Goeppert's and Mr. Binney's own figures. Mr. Binney's describes 

 his new specimen as having a radiating woody cylinder, imme- 

 diately within which is a second series of large vessels not arranged 

 in radiating wedges, and which Mr. Binney says is "something like 

 a medullary sheath, enclosing a medulla composed of very small 

 and short barred tubes or utricles, in which are mingled large 

 vascul.ir tubes or utricles." Though this use of vague terms 

 renders the sense obscure, I presume tirat Mr. Binney simply 

 means that in the medulla of his plant a vascular cylinder 

 encloses a cellular medulla, or, in other woids, that his specimen 

 has a Diploxyloid axis. That Mr. Binney possesses a specimen 

 having the above structure, and giving off rootlets from its 

 periphery, I have no reason for doubting, since in the memoirs 

 already quoted I have described a similar structure under the 

 name of Dif-loxylon stipnarioidcum, and respecting which I 

 make the following observations : — "It is possible that the plant 

 may, like Sligmaria, prove to be the uppermost pait of a root of 

 some of the other forms" {i.e. of Lepidodendioid stems), 

 " though I have never yet found it associated with any rootlets, 

 and it may be a fragment from the base where stem and roots 

 united " (loc. cit. p. 239). I arrived at the above conclusions 

 because I found in the specimen described, evidence that large 

 rootlet bundles were given off fiom the woody zone as in the 

 true Stigmaria. But I affirm that out of hundreds of Stigmaiian 

 fragments that I have examined, I have only found two pos- 

 sessing this structure, and I unhesitatingly express my conviction 

 that Air. Binney's specimen is another example of an equally 

 rare type, both being entirely distinct from Stigiiiaria ficoidcs., to 

 which latter plant alone is referable Mr. Binney's previously pub- 

 lished figures, M. Goeppert's description and figures of which 

 Mr. Binney approves, and mine which he rejects. 



Mr. Binney proceeds to say : "The size of these large vascular 

 tubes or utricles in the medulla exceeding .inything so far as his 

 knowledge extended, hitherto observed in fossil plants, shows 

 '.hat it was easily decomposed, and thus accounts for the general 

 absence of the medulla in Sigillaria and its roots." To this rea- 

 soning I must altogether demur. Size has nothing whatever to 

 do with the preservation of the tissues in fossil plants. Vascular 

 structures strengthened by transverse bars of lignine are equally 

 well preserved, whether they are large or small. The medulla of 

 Stigmaria disappeared or became much disorganised because it 

 consisted of an unusually delicate cellular tissue with extremely 

 thin walls. This tendency to decay was more manifest towards 

 the centre of the medulla than at its circumference. Specimens 

 on the table exhibit this peripheral part of the cellular medulla 

 in ex<iuisite perfection, giving oflF its characteristic cellular pro- 

 longations constituting the medullary ra) s, as described in ray 

 memoir. And yet this beautiful cellular tissue occupies the posi- 

 tion which Mr. Binney says was occupied by " large vascular 

 tubes or utricles." The specimens refeiTcd to showing these 

 conditions constitute unanswerable facts. 



Mr. Binney correctly notes the resemblance of the inner vascu- 

 lar cylinder in his specimen to his "medullary sheath." I have 

 already said the same thing in several of my memoirs, and M. 

 Brongniart said it before either of us. But this very homology, 

 if correct, indicates the probabiUty of Mr. Binney's specimen 

 being a fragment derived from the junction of stem and root 

 rather than a true root, since in living plants possessing a 

 medullary sheath, that sheath, as every botanist knows, is never 

 prolonged into the true roots, for the simple physiological reason 

 that its origin is directly connected with that of the leaf forma- 

 tions of the ascending axis. 



As I have already observed, M. Goeppert's and Mr. Binney's 

 previous figures represent a structure altogether different from 

 that now described by Mr. Binney. Instead of the continuous 

 inner vascular cylinder of the latter, M. Goeppert's figure displays 

 two detached, unsymmetrically arranged, vascular bundles in the 

 interior of the medullary cavity. 1 have already affirmed my 

 conviction that these belong to intruded rootlets of a Stigmaria, 

 and are in no respects part of the true medullary axis. On the 

 other hand, Mr. Bmney says that "they are certainly not intruded 

 rootlets, as anyone who examines the learned author's plates can 

 satisly himself." On this point Mr. Carrulhers writes to me on 

 Nov. 2 : "No one who is accur.tomed to sections of Stigmaria 

 can fail to see that Goeppert has mistaken the accidental rootlets 

 of Stigmaria penetrating the decayed axis for an organic part of 

 that axis." I may allow this opinion of an experienced botanist, 

 with which I wholly concur, to neutralise that of Mr. Binneyj 

 who further says: "It is veiy improbable that they" (i.e., 

 Goeppert's vascular rootlets) "had ever been intioduced into 



the axis after the pith had been removed." To this I reply that 

 it is an extremely rare thing to find any such axis which does 

 not contain more or less of these rootlets. My cabinet is full of 

 such examples, and in two specimens on the table, one of which 

 has been lent me by Capt. J. Aitken, of Bacup, similar rootlets 

 not only exist in the central axis, but have penetrated the medul- 

 lary rays as in M. Goeppert's specimen. 



Mr. Binney, referring to my comments upon his previous 

 memoir, says that in "that memoir mention is only made of the 

 large vascular bundles found in the axis, without calling them 

 vascular or any other vessels. " I do not very clearly understand 

 what this sentence means, but I presume it is intended to imply 

 that Mr. Binney never aflSrmed that the pith of Stigmaria con- 

 tained vascular tissues, .ind that I have misrepresented him in 

 stating that he had done so. I can only answer this by giving 

 Mr. Binney's words : — "The most important circumstance thus 

 developed is the existence of a double system of vessels in Stig- 

 maria, first shown by Goeppirt, and the consequent approach in 

 this respect to Diplcxylou, Corda. In Diploxylon, however, the 

 inner system forms a continuous cylinder, concentric with and 

 in juxtaposition to the wedges of wocd forming the outer; while 

 in Stigmaria the same inner system is broken up into scattered 

 bundles, apparently unsymmetrically arranged in the medullary 

 axis or pith of the plant" (Quai-/erly Journal oj the Geological 

 Society, vol. xv. p. 17) ; and on p. 78 of the same memoir, de- 

 scribing the specimen represented by Fig. 2, he says, "The axis 

 is filled with eleven or twelve large vessels of circular or oval 

 form," and the same structurts are again spoken of as "vessels" 

 no less than six times in the next seventeen lines, with the 

 further remark that "altogether these angular vessels remind me 

 somewhat of the vascular tissue in the middle of Anabathra " 

 (loc. cit., p. 78). It is true that in two places Mr. Binney 

 applies to these structures the teim " utricles," by which, I pre- 

 sume, he means cells ; but such a term, applied to such tissues, 

 is equally applicable to sll known hbro-vascular structures, and 

 is simply equivalent to saying that scalariform vessels have no 

 existence. 



I have entered into these details because by promulgating 

 vague and groundless doubts respecting woik alieady carefully 

 done, Mr. Binney's communication tends to re-introduce con- 

 fusion into questions that have been virtually settled. It does 

 this through failing to discriminate between things that differ. 

 His introductory remarks refer to the common Stigvtaria jicoides, 

 whilst his justification of those rercarks rests upon a plant of a 

 very different character, and which I am absolutely certain is 

 not the common form of Stigmaria. 



VEGETATION OF THE LIBYAN DESERT 

 TN Dr. Ascherson's report on the vegetation of the Libyan 

 -^ Desert, publi: hed in the Botaniscjic Zeituitg, there are some 

 interesting notes on the fall and renewal of the leaves of deciduous 

 trees. In our climate we have little difficulty in understanding the 

 distinction between evergreen and deciduous trees and shrubs, 

 because the greater part of those that change their leaves cast the 

 old ones in autumn or early winter ; and evergreens with flat 

 leaves have them more or less coriaceous. But ev«i with us 

 there is a gradual transition from evergreen to deciduous through 

 Eunon\mus europa:us and Ligustium lulgare, both of which 

 have strictly evergreen congeners in Eunonyinus japonicus and 

 Ligusirum japonicnm. Some few years ago Hoffmann started 

 a theory that sempervirence could be artificially produced, and 

 there is no doubt that climate influences to a great extent the 

 length of the period during which really deciduous species hold 

 their foliage ; but it appears far more probable that these are 

 physiological peculiarities not altogether dependent upon cli- 

 mate, as we find evergreen and deciduous species growing in the 

 same regions and under precisely similar conditions. .Some 

 evergreens do not change their leaves at all, and even retain 

 them for many years or all their lifetime ; Arauearia imbrieata, 

 for example. 'Ja.xoJium distichuiit, one of the few deciduous 

 Conifeije, offers a very curious phenomenon, inasmuch as the 

 ultimate branchlets are deciduous. The observations chronicled 

 by Dr. Ascherson ^gree almost entirely with our own experience. 

 On his outward journey he traversed 25" of lat. in less than a 

 month, which gave him an excellent opportunity for studying the 

 conditions of the same species under very diverse climates. Thus, 

 in the plains of Lombardy many deciduous trees, and especially 

 Morus alba, were still partially covered with foliage on the 19th 



