OCTOBKB 1!>. 188;3.1 



SCIENCE. 



633 



cal friends group the various structures contained in 

 plants into several ' appareils,' ' distinguished by the 

 functions which tliose structures have to perform. 

 Amongst others, we find the ' appareil de souliens,' 

 embracing those hard, woody tissues which may be 

 regarded as the supporting skeleton of the plant, aiul 

 the 'appareil conducteur," which M. van Tieghem 

 describes as composed of two tissues, — " le lissu 

 cribliS qui transporte essentielleraent les matieres in- 

 solubles, et le tissu vasculaire qui conduit I'eau el les 

 substances dissoutes." Wilhoutdiscussing the scien- 

 tific limits of this definition, it sufiSces for my pres- 

 ent purpose. In nearly all flowering plants these two 

 'appareils' are more or less blended. The support- 

 ing wood-cells are intermingled in varying degrees 

 with the sap-conducting vessels. It is so, even in the 

 lower gymnosperms; and in the higher ones these 

 wood-cells almost entirely replace the vessels. It is 

 altogether otherwise with the fossil cryptogams. The 

 vascular cylinder in the interior of the Calamites, for 

 example, consists wholly of bart-ed vessels, a slight 

 modification of the scalariform type so common in all 

 cry])togam3. Xo trace of the ' appareil de soutiens ' 

 is to be found amongst them. The vessels are, in the 

 most definite sense, the 'appareils conducteurs' of 

 these plants. No such absolutely undifferentiated 

 unity of tissue is to be foiuid in any living plants 

 nther than cryptogams. 



But these Calamites, when living, towered high 

 into the air. My friend and colleague, Professor Boyd 

 Dawkins. recently assisted nie in measuring one 

 found in the roof of the Moorside colliery, near Ash- 

 ton-under-Lyne, by Mr. George Wild, the very intelli- 

 gent manager of that and some neighboring collieries. 

 The flattened specimen ran obliquely along the roof, 

 each of its two extremities passing out of sight, bury- 

 ing themselves in the opposite sides of the mine. Yet 

 . the portion which we measured was thirty feet long; 

 its diameter being six inches at one end, and four 

 inches and a half at the other. The mean length of 

 its internodes at its broader end was three inches, 

 and at its narrower one an inch and a half. What 

 the real thickness of this specimen was when all its 

 tissues were present, we have no means of judging; 

 but the true diameter of the cylinder represented by 

 the fossil when uncompressed has been only four 

 inches at one end of the thirty feet, and two inches 

 and a half at the other. Whatever its entire diam- 

 eter when living, the vascular cylinder of this stem 

 must have been at once tall and slender, and conse- 

 quently must have required some 'appareil de sou- 

 tien' such as its exogenous vascular zone did not 

 supply. This was provided in a very early stage of 

 growth by the introduction of a second cambium- 

 layer into the bark; which, tliough reminding us of 

 the cork-cambium in ordinary exogenous stems, pro- 

 duced, not rork, but prosenchymatous cells.''^ In its 

 youngest slate, the bark of the Calamites was a very 

 loose cellular parenchyma; but in the older stems 

 much of this parenchyma became enclosed in tlie pro- 

 soncliymalous tissue referred to, and which appears 



' Vnn Ticghcm, TralK; ilc bolanlqile, p. 679. 

 > M< inoir Ix.. pi. XX., lign. 14, 1.% 18, 19, and 2U. 



to have constituted the greater portion of the ma- 

 lured bark. The sustaining skeleton of the plant, 

 therefore, was a hollow cyliiuler, developed centrifu- 

 gally on the inner side of an enclosing cambium- 

 zone. That this cambium-zone must have had some 

 protective periderm external to it, is obvious ; but I 

 have not yet discovered what it was like. We shall 

 find a similar cortical provision for supporting lofty 

 cryptogamous stems in the Lepidodendra and Sigil- 

 lariae. 



The carboniferous rocks have furnished a large 

 number of plants having their foliage arranged in 

 verticils, and which have had a variety of generic 

 names assigned to them. Such are Asterophyllites, 

 Sphenophyllum, Annularia, Bechera, Hippurites, and 

 Schizoneura. Of these genera, Sphenophyllum is 

 distinguished by the small number of its wedge- 

 shaped leaves ; and the structure of its stems has been 

 described by M. Renault. Annularia is a peculiar 

 form, in which the leaves forming each verticil, in- 

 stead of being all planted at the same angle upon the 

 central stem, are flattened obliquely nearly in the 

 plane of the stem itself. Asterophyllites differs from 

 Sphenophyllum chiefly in the larger number and in 

 the linear form of its leaves. Some stems of this 

 type have virtually the same structure 'as those of 

 Sphenophyllum, — a structure which differs wideJy 

 from that of the Cal.araites, and of whMi, consequent- 

 ly, these plants cannot constitute the leaf-bearing 

 branches. But there is little doubt that true cala- 

 mitean branches have been included in the genus 

 Asterophyllites. I have specimens, for which I am 

 indebted to Dr. Dawson, which I should unhesitat- 

 ingly have designated Asterophyllites but for my 

 friend's positive statement that he detached them 

 from stems of a calamlte. Of the internal organiza- 

 tion of the stems of the other genera named, we know 

 nothing. 



.It is a remarkable fact, that notwithstanding the 

 number of yourig calamitean shoots that we have ob- 

 tained from Oldham and Halifax, in whii-h tin; struc- 

 ture is preserved, we have not met willi one with the 

 leaves attached. Tliis is apparently due to the fact 

 that most of the specimens are decorticated ones. 

 We have a suflicient number of corticated specimens 

 to show us what the bark was, but such specimens 

 are not common. They clearly prove, however, that 

 their bark had a smooth, and not a furrowed, exter- 

 nal surface. 



There yet remains for consideration the nimierous 

 reproductive slrobili, generally regarded as belonging 

 to plants of this class, Equisetinae. We find some 

 of these strobili associated with steins .ami foliage of 

 known types, as in Sphenophyllum;- but we know- 

 nothing of the internal organization ot these sphc- 

 nophylloid strobili. We have strobili connected with 

 steins and foliage of Annularia,-' but we are equally 

 ignorant of the organization of tliese. So far as that 



• Memoir, pari v., pi. l.-v.; nnd part ix., pi. xxi., Ilg. 32. 



■ I^squcreux, Coal Dora of Pennsylvania, pi. II., fig. ftSJ. 



• I'cber die Iruclitiihren von .\nnularla spbcliuphylloldiH. 

 \-on T. Stcrzul. ZeltBclir. d. deutschen grolog. genellKcliafl.. 

 .lahri;. 18R2. 



