216 Linncean Society. — 



the interior bundles taking a flexuose direction. In the succeeding 

 leaves there are no simple trachese, but numerous tracheae form 

 bundles running parallel to each other as far as the extremities of 

 the leaves, and giving off lateral and transverse branches vv^hich 

 anastomose in a very beautiful manner. These vascular bundles 

 also descend as far as the base of the bulb. Above they are formed 

 entirely of trachese ; lower down the trachese are accompanied on 

 the outer side by dotted vessels, which extend upwards to penetrate 

 the leaves and downwards to communicate with the root. In the 

 roots the vascular system is composed of a certain number of bundles, 

 parallelly disposed with admirable symmetry, among which are seen 

 dotted and scalariform vessels, but no true trachese. A great number 

 of microscopical observations made on various plants under different 

 circumstances have confirmed these views, which Dr. AUemao con- 

 siders unquestionable. 



The paper was accompanied by a series of notes by Mr. Miers, 

 in which, from his knowledge of his antecedent researches, published 

 in the Proceedings of the Vellozian Society, he states it to have 

 been the object of Dr. AUemao to test the validity of the theory first 

 propounded by Du Petit-Thouars, and more recently modified and 

 supported by Gaudichaud, which maintains, contrary to the views 

 of Mirbel and others, that all the woody fibres of the stem proceed 

 from the nascent leaf-buds and thence descend to the radicular ex- 

 tremity of plants. Dr. AUemao believes that his observations in no 

 degree tend to support this theory. He takes as an example the 

 Cucurbita Pepo, in which the dotted vessels are extremely large and 

 conspicuous. In this plant no reticulated vessels are found in the 

 last-formed leaves or in the internodes near the termination of the 

 stem, although they exist in the lower and older leaves. He ob- 

 served spiral vessels only in the stems and leaves as low as the 9th 

 or 10th axil from the extremity of each branchlet ; from that point 

 as low as the 14th and 15th axils, other vessels are observed in the 

 stem only ; but below this point he found them in the stem, and 

 more especially in the leaves, proving, as he believes, that all reticu- 

 lated and dotted vessels ascend through the stem before they find 

 their way into the leaves, in the progress of their growth upwards. 

 He thinks that the formation of a circular tumour in the trunk of 

 dicotyledonous plants above the line of a ligature tightly tied around 

 it may be accounted for by reasoning on the facts which he con- 

 ceives himself to have established, viz. that in the development of 

 the vascular fibres of the stem, there always exists a vital centre from 

 which they extend themselves in two opposite directions. This 

 vital centre may be fixed, moveable, or accidental ; fixed in woody 

 fibres, moveable in trachese, and accidental in all adventitious forma- 

 tions. If, for instance, we take a cutting of any young branchlet, 

 in which no natural bud is distinguishable, and plant half of it in the 

 ground, several adventitious vital points make their appearance, the 

 lowermost of which give out rootlets, and the uppermost leaf-buds. 

 In this case, vital points or centres make their appearance in the vital 

 zone of the cutting, which would never have existed in the natural 



