ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 509 



very different types of structure, supports the theory, which he has 

 previously put before the Academy, as to the foliar nature of the stem. 

 Each leaf-primordium consists of three meristems, an epidermal, a cortical 

 which follows the epidermal, and a vascular. At the leaf -base the three 

 meristems are continuous with those of leaf-primordia above and below 

 and also laterally with those belonging to the same cycle. The stem- 

 segments corresponding to their respective leaf arise by cell-division in 

 the respective vascular meristems. 



Bundle Arrangement in the Petiole and Leaf- Veins in Dicoty- 

 ledons.* — M. Col seeks to explain the bundle arrangement in the leaf- 

 stalk and veins. In all leaves of dicotyledons the nerves and stalk 

 show in transverse section an arc of phloem and xylem, either con- 

 tinuous or divided into bundles ; in many cases there are also one or 

 several bundles placed above this arc. The upper system may unite by 

 its edges with the sides of the lower arc ; the two together constitute 

 a stele. The author suggests that only the bundles of the arc are in a 

 normal position, and they alone correspond to the vascular circle of the 

 stem. The region in which the upper (anterior) bundles are more or less 

 tardily developed, is homologous to the pith of the stem — it is the upper 

 peridesm of Van Tieghem in a slightly extended sense. For convenience 

 of description, we can differentiate the bundles placed above the 

 normal lower arc into anterior (or upper) bundles and medullary bundles 

 proper. The author admits, however, that it is impossible to conceive 

 any nomenclature for the foliar bundles which shall embrace and satisfy 

 all the intermediate arrangements. 



Existence of a Pith in the Leaf-Stalk of Phanerogams. f — 

 M. Bouygues points out that in addition to the three fundamental 

 regions, epidermal meristem, cortical meristem, and vascular meristem, 

 which the researches of Bonnier and Flot have demonstrated in the 

 young leaf, there is also a definite pith. In a young petiole the whole 

 of the vascular meristem is not used up to form the procambium strands. 

 At the base of the petiole there is a clearly defined remainder in the 

 upper surface of the organ above the procambium strands which corre- 

 sponds by its situation and perhaps also by its origin with the pith of 

 the stem. 



In some cases this meristem is separated from the epidermis by a 

 sub-epidermal layer, which does not remain simple. The form of its 

 elements and its radial division suggest its equivalence to the cortical 

 meristem ; but this layer early becomes the seat of rapid tangential 

 divisions and gives rise to the supplementary vascular meristem. The 

 question then arises whether this layer is cortical or a part of the normal 

 vascular meristem. The author has in -a previous memoir described it 

 as cortical. M. Col J however, on purely anatomical grounds, regards 

 all the sub-epidermal tissues on the upper face, with or without bundles, 

 as equivalent to the pith of the stem, an interpretation which does not 

 agree with the results of M. Bouygues' researches. 



Unipolar Stele in Rootlets of Trapa.§ — C. Queva describes the 

 anatomy of the roots of Trapa natans. The stele in the main root is 



* Comptes Rendus, cxxxvi. (1903) pp. 516-8. f Tom. cit., pp. 771-1. 



X See above. § Comptos Rendus, cxxxvi. (1903) pp. 826-7. 



Aug. 19th, 1903 2 l 



