HARD WICKE'S SCIENCE- G OSSIF. 



127 



'*' diploxylon." " Diploxylon again shades off into 

 the ordinary forms of Lepidodendron, which have 

 lost the central portion of their medulla." He also 

 says, in another place, in reference to a series of 

 specimens of this plant from Burntisland, " Lepido- 

 dendra are the twigs and branches of the diploxylon 

 stems." It will be seen from the above remarks that 

 diploxylon and SigiHaria vascularis are alike in their 

 internal structure, with this exception, that in the 

 former, the tissues of the centre of the medulla are 

 absent, while in the latter tliey are present. 



This difference may possibly be a specific character, 

 or it maybe a mere accidental feature due to the 

 varying processes of fossilisation. But it is important 

 to note that both these plants occupy a midway 

 position between the lower forms of lepidodendrons 

 on the one hand, and the more highly-organised 

 sigillaria on the other. I have already observed that 

 specimens of the real ribbed sigillarias, as distinct 

 from the Favularian type, are exceedingly rare. 

 Some time ago, however, I had the good fortune to 

 come across a real sigillaria, of which I shall now, in 

 •conclusion of this paper, give a brief description. 



StgiHaria reniformis. This well-known plant is 

 occasionally met in our coal-balls, but generally, like 

 all the other species of true sigillaria, it is only 

 represented by its epidermal layer. This specim en 

 was in a fair state of preservation, although some- 

 what compressed, and the centre badly pyritised, so 

 as to render it doubtful whether I could grind a 

 section of that part transparent enough for the micro- 

 scope. The specimen was about l\ inches square by 

 % inch thick. In order to make the most of it, I cut it 

 up into four pieces, two of these I reserved for longi- 

 tudinal sections of the bark, one for transverse, and 

 the other for longitudinal sections of the centre, I 

 managed to prepare a good series of longitudinal 

 sections of the bark and then proceeded with great 

 caution to cut transverse sections of the centre. I 

 managed to cut three sections, one of which flew into 

 pieces in cutting, another I ground slowly away with- 

 out being able to get it transparent. The last section, 

 notwithstanding the greatest care, wasted away till 

 only one half of the central portion was left, before I 

 succeeded in reducing it sufficiently thin for micro- 

 scopic examination. At length I obtained my object, 

 and although the section is here and there somewhat 

 obscured by black sjDots of iron pyrites, yet sufficient 

 remains to show the structure of the central medulla 

 and the ligneous cylinder. The centre of the medulla 

 is composed of cellular tissue, and this is surrounded 

 by a "medullary cylinder " which is composed of 

 vascular tissues. This is surrounded by a ligneous 

 cylinder, formed of scalariform vessels. 



This is the only undoubted transverse section of 

 the centre of a true sigillaria that I have seen, yet in 

 no respect does it differ from what obtains in Sigil- 

 laria vascularis. 



Indeed so exact is the resemblance, that I have not 



deemed it necessary to give a drawing of it, as fig?. 

 76 and 77, representing a transverse section ot" 

 Sigillaria vascularis^ will also c([ually answer for this 

 transverse section of S. renifonuis. 



I have a tangential section of the same plant, 

 showing two of the "ribs " or ridges. Before I began 

 to grind the specimen down to a level surface, the 

 well-known pairs of kidney-shaped markings so cha- 

 racteristic of this species were plainly visible, but as 

 these cicatrices are slightly raised above the level of 

 the ridges, and invariably go into one a little below 

 the surface, it is almost impossible to obtain thes^ 

 reniform markings in our preparations, especially in 

 a small plant like this. In larger plants of course 

 and under favourable conditions, we might succeed 

 in making a section a single ridge, showing one 

 or two pairs of these markings. I have such a 

 specimen in my cabinet. 



The main fact which this specimen is intended to 

 show, is that it is a real sigillaria of the ordinary kind, 

 having the usual ridges and furrows and markings 

 peculiar to these plants. The next point is to show 

 the long fusiform or the spindle-shaped vessels, which 

 overlap one another in such a way as to leave no 

 space between them, and thus form a true prosen- 

 chyma or woody tissue. I have already point-ed out 

 that the outer part of the bark or bast layer, in 

 Lepidodendron selagiiioidcs, consists of the same kind 

 of fusiform vessels. In Sigillaria vascularis the greater 

 portion of the bark is formed of them, and in these 

 sections of Sigillaria reiiiforinis the whole of the bark 

 seems to be composed of these fusiform vessels. 



The centre of the, medulla is composed of barred 

 cells, on each side of which are the vessels forming 

 the medullary cylinder, which is again enclosed by 

 the ligneous cylinder. 



I have a section across the ligneous zone, showing 

 the manner in which the medullary rays are inter- 

 spersed among the long barred vessels composing it. 

 The medullary rays originate in the small spiral 

 vessels forming the "medullary sheath" and pass 

 through the ligneous zone on their way to the 



leaves. 



( To be continued.) 



Chelonia Caja. — Sometimes, although rarely, 

 two broods of this insect will occur in one year. It 

 happened so once in my experience. Owing to a mild 

 winter and spring, the "woolly bears" underwent 

 their transformation into "tiger-moths" earlier than 

 usual. The caterpillars produced from the eggs which 

 the first brood of moths laid grew rapidly, and having 

 attained their full size spun up about the 15th of 

 September ; the first moth came out upon September 

 27th, the others in October, and (one) the begin- 

 ning of November. They were all much smaller than 

 the usual size of this insect, measuring from one inch 

 ten lines to two inches one line in expanse of wings. 

 —Albert Waters, B.A. 



