lO Contributions towards Establishing the General Character 



plants which oflPer an exception to the general rule, and which, in this 

 respect; are allied with the fossils. Thus Mohl has shewn that in Ephe- 

 dray which approximates to the Conifers in many respects, the ligneous 

 vessels are discigerous on the whole of their walls. 



Brongniart also points out an analogous character in Zamia integrifo- 

 lia of South America.* The same is also to be found in plants lower in 

 the vegetable series, as the Ferns and the Lycopods of existing creation, 

 and in Lepidodendron, Psaronius, and others belonging to the car- 

 boniferous epoch. The discs on the walls of the ligneous vessels of 

 ConifercB and CycadacecB are round or oval; but in Zamia integrifolia, they 

 have more resemblance to the transverse and reticulating bars of Sigil- 

 laria elegans in being considerably elongated. In the latter, however, 

 they are more regular. This regularity and elongation of the bars are 

 still more developed in the Ferns and the Lycopods. 



It follows from these facts, that Sigillaria elegans^ Anabathra, and Stig- 

 maria, are allied to the Gymnospermous Dicotyledons by the uniformity 

 of the tissue composing their ligneous and vascular systems ; and to the 

 Vascular Cryptogams by the regularity and form 'of the bars on the 

 walls of the vessels of those systems. 



It has been previously mentioned, that in Sigillaria elegans the vascu- 

 lar system, or medullary sheath, is formed of a broken but regular circle 

 of bundles, and that the constituent vessels are arranged irregularly, 

 and not in radiating series like the vessels of the ligneous cylinder. It 

 may also be added, that these bundles are slightly separated from the 

 ligneous cylinder on the inside of which they are placed. According to 

 Brongniart, nothing of the kind is to be found in the allied fossils Stig" 

 . maria and Anabathra, nor does it appear that a similar character occurs 

 in any recent plants. In some of the latter, however, we have instances 

 of vascular bundles being widely separated from the ligneous cylinder, 

 and dispersed irregularly throughout the pith. This certainly appears 

 to be a modified arrangement, and as such may be so far an analogous 

 case. Very different families display this arrangement ; Mirbel has ob- 

 served it in Nyctago liortensis, and in some umbelliferous plants ; Schultz 

 has remarked it in Piperacece, and in several Nyctaginacece ; Brongniart 

 has observed it in various Echinocacti, in Echeveria grandijlora, and in 

 Plantago princeps ; Decaisne has studied it in Phytolacca dioica, and in 

 various Melastomacece ; he is convinced, however, that it does not occur 

 in some other plants of the same families, nor even in all the plants of 

 the same genus. In short, it appears to be often absent in closely al- 

 lied forms ; thus, among the Cactuses^ it exists in certain species, and 



♦ Brongniart thinks it probable that the other American species, or the true 

 Zamice, will be found to[possess the same character ; in this respect they will differ 

 from the Australian and African Cycas and Encephalartos, which appear to have 

 their vessels marked with discs only on those walls which coincide with the direc- 

 tion of the medullary rays. 



