284 PROCEEDINGS OF SOCIETIES. 



' medaliary slieatli' in recent plants. The consideration of the extinct 

 forms of higher Cryptogams showed him tliat tlie term Acrogens must be 

 given up, and led him to propose their division into two groups, correla- 

 tive with those of Phanerogams. Amongst Cryptogamic Exogens he 

 would include Equisetacece, Lycopodiacea, hoetacefs. The Ferns would 

 constitute the Endogeus. Mr. Carruthers congratulated Professor Wil- 

 liamson on his acquaintance with Professor King's paper, which he (Mr. 

 Carruthers) had been the means of bringing to his notice. The so-called 

 ' vascular pith,' according to his view, was entirely composed of vessels, 

 some very short ; anything like the truncated cellular tissue shown in the 

 diagram was not shown by the specimens. Dr. Hooker had suggested 

 the term ' utricles' for these, as a kind of compromise between vessels and 

 cells. The structure of Fern stems was precisely that of Stigmaria ; 

 from the vascular cylinder pass off vascular bundles carrying,' with them a 

 considerable quantity of cellular tissue. In llywenoj)hjUam, however, 

 there was the opposite arrangement, a vascular axis instead of a cylinder; 

 so that, according to Professor Williamson, Ferns woidd be split up into 

 two groups. The vascular bundles were scattered in some Lycopodlacece, 

 but in Lycopodiam they were united into a central axis, and this was 

 precisely the same as in Lepldodcndron. Classification must be based 



entirely on the reproductive organs. Professor Dickson thought the 



' vascular pith' was undoubtedly a central axis. Be should like to know 



what distinct evidence there was of the existence of a cambium layer. 



Prof. McNab could not agree with Prof. Williamson in his interpretation 

 of the structure of these stems. Botanists are all agreed in this, that 

 Lepldodendrou and their allies are closely related to the Lycopods. Now we 

 know that the Lycopods, like the Ferns, have closed fibro-vascular bundles 

 Avhich can only grow for a certain time, and then, all the cambium being 

 converted into permanent tissue, growth must cease. The key to these 

 structures is to be met with in Lycopndinm ChanKTcyparissus, in which 

 we have a cylinder of wood-cells surrounding the central cylinder of united 

 fibro-vascular bundles. This cylinder of wood-cells represents and is a 

 mere modification of the cellular tissue met with in the ordinary stems of 

 Lycopods. In this wtiy it follows that the central portion is not a pith, 

 but consists of the central group of fibro-vascular bundles. It also follows 

 that the wood cylinder in these stems is not the homologue of the wood 

 cylinder of an ordinary exogen. He thought the classification of these 



plants proposed by Prof. Williamson quite untenable. Prof. Thiselton 



Dyer was glad that Prof. Williamson had at last brought his jiapers to 

 the section where they could be properly discussed. He thought it was 

 a great mistake to dissociate, as was so frequently done, the study of 

 extinct from that of recent forms. The proposed arrangement seemed to 

 him to violate all the canons of natural classitication. It was impossible 

 to separate Eqiusetacefe from Ferns. It was a caricature of evolution to 

 hint any analogy between Prof. Williamson's ' medullary zone ' and the 

 medullary sheath. 



{To he continued.) 



Belfast Naturalists' Field Club. — The third excursion for this 

 season took place on Saturday, July 8th, the locality selected being the Cave 

 Plill Quarries and Deer Park. The sections exposed here are very instruc- 



