ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 317 



Strvicture and Development. 



Vegetative. 



Persistence of the Alternate Structure in Cotyledons.* — G. 

 Chauveaud refers to an interpretation of the relation between collateral 

 and radial bundles, which formed the subject of a previous note in the 

 Comptes Bendus, 1901. The collateral structure characteristic of the 

 leaf is not primary to the same degree as the alternate arrangement 

 which characterises the root. It represents the last phase of evolution 

 of the conducting apparatus, the alternate arrangement representing the 

 first phase, and the two being connected by an intermediate phase. In 

 all the roots of the higher plants where the conducting apparatus under- 

 goes a complete evolution, there appear (1) the alternate phase, (2) the 

 intermediate, (3) the superposed pbase. If instead of following the 

 development in the root w T e ascend the plant axis, we find a greater or 

 less acceleration of the development, which at a certain level finds ex- 

 pression in the suppression of the two first phases. When development 

 is greatly accelerated, as in the haricot, the suppression occurs suddenly 

 in the neighbourhood of the neck. When on the contrary it is less 

 rapid, as in onion and Pinus maritima, the earlier phases persist not 

 only in the tigellum but also in the cotyledons. That is to say there 

 appear in a leaf the same phases already indicated in the root : 

 (1) alternate, (2) intermediate, (3) superposed, a proof that the super- 

 posed arrangement in the leaf represents only the last phase of evolution 

 of the conducting apparatus. In a recent note,f the presence of the 

 alternate arrangement has been described in the cotyledons of several 

 Labiatre. In Lamium album and other members of. the order, the two 

 primary wood bundles of the radicle pass into the cotyledons, remaining 

 in the same plane, that is, the plane of symmetry of the cotyledons. 

 The bundles' do not divide, and no rotation occurs. At a later stage, 

 the first formed elements disappear and only superposed elements are 

 found. 



Lignification of Subterranean Organs in Plants of High Re- 

 gions. J — A. Dauphine describes some peculiarities in the structure of 

 the wood of the roots and rhizomes of some herbaceous plants, which 

 when adapted to an alpine climate show a considerable development, 

 living for many years and forming organs of reserve during the period 

 when aerial growth is suspended ; successive layers of wood are formed 

 each year. In many families, Ranunculacese, Caryophyllaceae, Rosacea, 

 Compositge, G-entianaceae and others, the lignification of the secondary 

 wood is irregular. Thus in Cherleria sedoides the wood forms a con- 

 tinuous ring surrounding a very reduced pith ; the vessels, which are 

 very numerous and of small calibre, are scattered in a cellulose paren- 

 chyma, and have but slightly thickened membranes which show no 

 trace of lignification ; the medullary rays and the annual layers are not 

 evident. A similar arrangement occurs in the rhizome and root of 



* Comptes R'-n lus, cxxxviii. (1904) pp. 768-72. 



t Op. cit., cxxxvii. (1903) p. 804. 



t Op. cit., cxxxviii. (1904) pp. 592-3. 



June 15th, 1904 z 



