ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 159 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Structure and Development. 

 Vegetative. 



Significance and History of Pine-needles. — J. Dufrenoy (Bot. 

 Oaz., 1918, 66, 439-54, 29 figs., 1 table) has studied pine-needles in 

 order to throw light upon their morphological significance. The present 

 work includes a brief account of their development, histology, physiology, 

 and pathology, and the writer concludes that morphological variations 

 are the result of physiological variations. The wide differences seen in 

 the phyllodes, juvenile leaves, scale-leaves, fertile leaves, and assimila- 

 tory organs are shown to be different features " of a unique ancestral 

 organ," resembling the gametophyte of ferns in possessing the three- 

 fold function of reproduction, assimilation, and protection. The phyl- 

 lodes of primitive coniferous trees were probably all fertile, but owing 

 to unfavourable ecological conditions some of them became sterile. In 

 support of this hypothesis reference is made to Pinus maritima, where 

 parts of the male flowers which have been exposed to a strong sea-wind 

 became sterile, and scales take the place of stamens. Studies of inter- 

 mediate and abnormal leaf -forms show the process of development to be 

 as follows: — 



Fertile (reproduction) | 



Green (assimilation) ->- juvenile leaf — short needle. 

 Storage of reserves -^ cotyledonary needle. 

 Self-protecting -^ scale. 



6 fertile leaf. 



V )) n 



Primitive organ / 



Thus needles are the physiological leaves of pines, differing from 

 ordinary leaves in being perennial and less fragile ; they last several 

 seasons and are adapted to the roughest weather and the most adverse 

 ecological conditions. S. G-. 



■'o' 



Significance of Resinous Tracheids. — S. J. Record {Bot. Gaz., 1918, 

 66, 61-7, 5 figs.) publishes the result of his investigations as to the 

 significance of the resinous tracheids previously described by Penhallow. 

 The " peculiar form " and " particular location " upon which the latter 

 laid such stress are readily understood in view of their origin. The close 

 association of the resin-plates with the medullary rays indicates the 

 origin of the resin, which is an excretion resulting from the metabolic 

 processes of the parenchyma cells ; such excretion is most abundant 

 when the cells are about to cease their vital functions and become 



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