246 Mr. H. O. Stephens on the Fungi and Cycadece the cells which form the wood develops 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, Mammil-laria simplex, Helleborus foetidus, &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 Sapindacece, 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 Phytocrene (Wall.), or of the analogous forms frequently oc-curring in the family of the Biffnoniacece, — forms which can-not be described by words, for which reason I cursorily refer to Lindley, ^ Introduction to Botany,' p. 79, 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
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