246 Mr. H. O. Stephens o?i the Fungi 



and Cycadece the cells which form the wood develope uni- 

 formly, and not as in many other kinds of wood separating into 

 prosenchyma and vessels. In many plants the earliest spiral 

 vessels of the medullary sheath, in consequence of the great 

 longitudinal expansion of the cells, become changed into an- 

 nular vessels, in which form they remain ; in other plants the 

 spiral vessels do not show this tendency, notwithstanding the 

 great extension they have to undergo ; they are then frequently 

 elongated with their cell to such a degree that they appear 

 only like a thread lying in an intercellular passage, and they 

 are very frequently entirely reabsorbed. This may be beauti- 

 fully observed in Opuntia monacantha, cylindrica, Maimnil- 

 laria simplex, Helleborus fcetidus, &c. May not this be the 

 reason why we in many cases no longer find genuine spiroides 

 in the developed stem, even in the corona medullaris ? 



The study of the organization of stems is still a boundless 

 field for careful research; so far as I know no one has yet 

 given a true explanation of that frequent formation in the fa- 

 mily of the Sapindace(B, where in one stem we meet with se- 

 veral centra for the formation of wood, only one of which oc- 

 cupies the axis of the stem. Likewise very little that is satis- 

 factory is known of the peculiar structure of the stem of the 

 Vhytocrene (Wall.), or of the analogous fonns frequently oc- 

 curring in the family of the Bignoniacece, — forms which can- 

 not be described by words, for which reason I cursorily refer 

 to Lindley, ^ Introduction to Botany,^ p« 7^^ fig* 36, where a 

 similar structure, stated to be from a Passiflora, is repre- 

 sented. 



XXVII. — On the Mycology of the neighbourhood of Bristol, 

 By Mr. Henry Oxley Stephens. 



To the Editors of the Annals of Natural History. 



Gentlemen, 



I DO not know whether you will consider the following My- 

 cological Notices of sufficient importance as to give them a 



