270 PKOGRESS OF MICROSCOPICAL SCIENCE. 



inquiry did not always run parallel, and the one great object of recent 

 researcli liad been to make them do so. Specimens throwing light on 

 the subject had been found at Arran, Burntisland, Oldham, Halifax, 

 Autun in France, and elsewhere, and uj)on these a host of observers 

 had been and still were working. It had long been known that most, 

 if not all, the coal plants belonged to two classes, known as the 

 Cryptogamia, or flowerless plants, and the gymnospermous exogens, 

 represented by the pines and firs. All recent inquiries added fresh 

 strength to this conclusion. One of the most important of these 

 groups was that of the Equiseta or horse-tails, and which were rejDre- 

 sented in the coal by the Calamites. The long cylindrical stems, 

 with their transverse joints and longitudinal gi'ooves, were shown to be 

 casts of mud or sand occupying the hollows in the piths of the living 

 l^lants. Each of these piths was surrounded by a thick zone of wood, 

 which again was invested by an equally thick layer of bark. Speci- 

 mens were shown in which, though the pith was only an inch in dia- 

 meter, the wood and bark combined formed a cylinder 4 inches thick, 

 giving a circumference of at least 27 inches to the living stem. But 

 there exist exami)les of the pith casts alone, which are between 2 and 

 3 feet in diameter. It was evident, therefore, he concluded, that the 

 Calamites became true forest trees, very different from their living 

 representatives — the horse-tails of our ponds and marshes. 



After describing the organization of these plants, the Professor 

 proceeded to describe the Lycopods of the coal-measures as represented 

 by the Lepidodendra, Sigillarise, and a host of other well-known plants. 

 The living Lycopods, whether seen at home or in tropical forests, 

 are dwarf herbaceous plants, but in the carboniferous age they became 

 lofty forest trees, 100 feet high, and 10 or 12 feet in circumference. 

 To enable such lofty stems, with their dense mass of serial branches 

 and foliage, to obtain nutrition, an organization was given to them 

 approaching more nearly to that of our living forest trees than to that 

 of any recent cryptogams. A succession of woody layers was added 

 to the exterior of those previously existing ; so that as the plant rose 

 into the aii- the stem became strengthened by these successive addi- 

 tions to the vascular tissue. As this process advanced it was accom- 

 panied by other changes:, producing a large central pith, and two 

 independent vascular rings immediately surrounding the pith, and the 

 relations of these various parts to the roots, and leaves, as well as to 

 the nutrition of the plants, were jjointed out. The fruits of these 

 Lycopods were then examined. The existence of two classes of spores 

 corresponding in functions to the stamens and pistils of flowering 

 plants, was dwelt upon, and one of these classes (the macrospores) was 

 shown to be so similar to the small objects found in coal, as to leave 

 no doubt that those objects were derived from the lei^idodendroid and 

 sigillarian trees which constituted the large portion of the forest 

 vegetation. 



Certain plants known as Asterophyllites were next examined. 

 The ferns were also reviewed, and shown to be as remarkable for the 

 absence of exogenous growth from their stems as the Calamites and 

 Lycopods were for its conspicuous presence. The structure of some 



