and on the Structure of Hydnora africana. 231 



I have in the first place to correct my own error respecting Rafflesia, in 

 various parts of the female flower of which 1 liave found spiral vessels of the 

 ordinary structure, consisting of a single, easily unrolled fibre; and on re- 

 examining the same specimen of the male flower respecting which my former 

 assertion was made, I found these vessels equally distinct. Professor Meyer has 

 already stated their existence in the procumbent stems or rhizomata of /^(;?«ora 

 triceps ; in which I have also found them in Hydnora africana, as well as in 

 other parts of the same species ; and in Cytinus they are still more obvious. 



I may also add, that wherever I have had specimens of Balanophorece in a 

 fit state for minute examination, I have never failed to find spiral vessels in 

 various parts of their tissue, particularly in Cynomorium coccineum and Helosis 

 guianensis*. 



* Although in Rafflesiacets and in the genera at present referred to Balanophorece, spiral vessels un- 

 doubtedly exist, in the greater number, indeed, sparingly, but in some cases in hardly reduced propor- 

 tion, it may still perhaps be alleged, by those botanists who have proposed to unite both families into one 

 natural class, that the vascular system of all these parasites is uniform and more simple than that of the far 

 greater part of Phsenogamous plants ; that the spiral or slight modifications of it is the only form of vessel 

 hitherto observed in any of them ; and that the large tubes or vessels, with frequent contractions, cor- 

 responding imperfect diaphragms, and variously marked surface, which have received several names, as 

 vasa porosa, punctata, vasiform cellular tissue, dotted ducts, &c., and which are so conspicuous in 

 the majority of arborescent Phsenogamous plants, have never been observed in any part strictly belong- 

 ing to these parasites. But even admitting the non-existence of the large vessels here referred to, 

 their absence will hardly be regarded as a sufficient reason for the union into one class of the two 

 families in question, especially when it is considered. 



First, That conformity in vascular structure, even when accompanied by peculiarity of tissue, does 

 not always indicate, much less determine, botanical affinity. ITiis is strikingly exemplified in Conifertt 

 and Winteranea, two families which, though so nearly agreeing in the uniformity and peculiarity of 

 their vessels, and in both of which the large tubes referred to are wanting, yet differ so widely from 

 each other in their organs of reproduction and in their leaves, that they may be regarded as placed 

 at opposite extremities of the scale of Dicotyledones . 



Secondly, That uniformity of vascular structure is not always found in strictly natural families. 

 Thus many tropical woody climbers exhibit remarkable peculiarities of vascular arrangement not ex- 

 isting in the greater part of the families to which they respectively belong, but which peculiarities 

 appear to have no influence whatever in modifying their reproductive organs. 



Thus also in Myzodendrou ' the whole woody tissue consists of vasa scalariformia, a peculiar struc- 



' Myzodendron of Banks and Solander, from fxvi^ew or fivi^o) sugo, and ^ipdpov, has been changed to 

 Misodendron by DeCandolle and all following systematic writers ; no doubt merely from a mistake as 

 to the intended derivation. Myzodendron, hitherto referred to Loranthacece, to which it is certainly 



