ZOOLOGY AND BOTANY. MICROSCOPY. ETC. 437 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 including Call-Contents. 



Polarity in Plant-cells.* — W. Marquette has stiulied the polarity 

 manifested by the cells of Isoetes lacustris, and is of opinion that neither 

 the kinoplasmic nor the dynamic theory is sufficient to account for the 

 behaviour of the polar structures. The latter can be readily distin- 

 guished at any period in the existence of the cell, and they are 

 undoubtedly differentiated structures of the cell which multiply by 

 successive fissions. The relations of these bodies and their movements 

 to the spindle fibres show that they are intimately connected with 

 spindle formation. The author thinks that it might be assumed that in 

 Isoetes there is transition from a cell with a well-defined centrosome, as 

 in some algae and fungi, to a cell without anything corresponding to a 

 centrosome as found in the spermaphytes. 



Structure and Development. 

 Vegetative. 



Function of Sieve-Tubes.f — M. Molliard has investigated the con- 

 ditions favouring the formation of sieve-tubes, with the purpose of 

 throwing light on their function. From experiments upon plants grown 

 exclusively in a mineral culture-solution, and others, under the same 

 conditions but with the addition of an organic substance such as 

 saccharose, it appears to be clear that the sieve-tubes are numerous and 

 well developed, while the wood is proportionately backward in develop- 

 ment, in direct relation to the supply of organic material. This is 

 especially to be noted in such plants as the Radish. By growing this 

 plant in a solution of glucose, the supracotyledonary region assumed the 

 characters of a rhizome, becoming packed with reserve organic material ; 

 at the same time the normal internal structures underwent change, the 

 wood being replaced by phloem with numerous sieve-tubes. 



Morphology of Stem of Dennsta^tia punctilobula.| — H. S. Conard 



makes a short contribution upon the stem of Demistaedtia pimctilohula. 

 The young stem is at first simple ; then two branches appear which at 

 once 'assume the adult form and lirauch freely. The earhest formed 

 stem is protostelic, having central xylem surrounded by parenchyma, 

 phloem, pericycle, endodermis, and cortex. The central xylem then 



* Beih. Bot. CentralbL, xxi. (1907) pp. 281-303 (1 pi.). 



t Comptes Rendus, cxliv. (1907) pp. 1063-4. 



X Johns Hopkins Univ. Circular, No. 5 (1906) pp. 95-8. 



