Biologie. — Cytologie und Befruchtung. 355 



entre 5 et 20 ctm. sous la surface. Les Le'gumineuses ä nodo- 

 sites et les plantes ä mycorhizes sont les vegetaux les plus 

 frequemment attaques. 



Le developpement du su^oir veritable est precede de la 

 formation d'un renilement parenchymateux renfermant un cordon 

 axile d'elements allonges. Les cellules superficielles situdes dans 

 le prolongement de ces derniers s'enfoncent dans les tissus de 

 l'höte, en meme temps que la differenciation ligneuse s'effectue 

 dans le renflement. 



Outre les su(;oirs simples qui n'ont qu'un seul renflement, 

 on trouve des suQoirs composes qui ont plusieurs renflements 

 superposes, dans le cas oü les tissus de Thöte sont tres 

 resistants. 



Le su^oir possede entre les tissus corticaux parenchymateux 

 et les faisceaux libero-ligneux, une zone caracteristique de tissus 

 ecrases. 



L'absorption se fait par des cellules penetrantes qui ont la 

 forme de poils absorbants et dont les membranes sont partielle- 

 ment lignifiees et aussi par le tissu liberien de forme palissadi- 

 que qui se met en contact avec le über de Thöte. 



C. Queva (Dijon). 



Harshberger, John W., The Relation of IceStormsto 

 Trees. (Contributions from the Botanical Laboratory of the 

 University of Pennsylvania. Vol. II. No. 3. p. 345 — 349. 

 1904.) 



Gives descriptions and statistics of two exceptionally se- 

 vere ice storms that visited the Philadelphia region in 

 February and December 1902. Common garden and street 

 trees were damaged in the following order: silver maple very 

 severely; weeping willow and Carolina populär less so, 

 beech, elm, hickory, white oak, and plane tree (Plataniis) 

 least injured. A brauch of oriental plane (Plataniis orlentaUs) 

 showed a weight ratio between brauch and its accumulated 

 ice of 1 : 100. J. M. Macfarlane. 



Watson, Cassius H., The Structure and Relation of the 

 Plast id. (Contributions from the Botanical Laboratory of 

 the University of Pennsylvania. Vol. IL No. 3. p. 336 

 —344. Plates 26, 27. 1904.) 



Starting with Macfarlane's Observation^ on Dlonaea, 

 the writer finds in a wide series of plants belonging to diffe- 

 rent groups of the vegetable kingdom, that the plastids of the 

 plant cell are linked with each other by fine threads that great- 

 iy resemble attenuate chromatin and that the plastids show a 

 structure closely resembling, if not identical with the nucleus 

 of the cell in which these plastids lie. „It seems therefore not 

 unnatural to suppose that plastids primarily represent nuclear 

 differentiations of the cell^ which have been separated off for 



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