igoS] CURRFNT LITERATURE 355 



mation of certain carbohydrates, suitable for forming the partition walls, into 

 gums rich in oxygen. Parasites and saprophytes affect the formation of gum only 

 by creating or enlarging rifts or wounds, hindering their recovering and recover)', 

 and so making possible the access of oxygen. Experimental proofs are adduced 

 for this view, whose probability is increased by many chemical considerations 

 C. R. B. 



Fixation of free nitrogen.— Dr. Charlotte Ternetz, baffled in an attempt 

 to identify the pycnidial fungi which belong to the endotrophic mycorhiza of the 

 Ericaceae, turned to a study of the ability of these fungi to fix free nitrogen when 

 grown in N-free cultures, ^s The fungi doubtless belonged to the genus Thoma, 

 and five species are described, derived from the roots of as many genera. These 

 all fix atmospheric nitrogen, though in very different amounts. The three from 

 Vaccinium, Oxycoccus, and Andromeda, while they work far less energetically 

 in this respect than most N-fixing bacteria, nevertheless gain the largest amount 

 of nitrogen of any known organisms in comparison with the amount of carbo- 

 hydrate consumed. Aspergillus nlger and PenkUlium glaucum hkcwise are 

 capable of fixing free N in small amounts, comparable with those yielded by the 

 other two Phomas from the roots of Tetralix and Erica. 



It may be that this action, relatively small when the fungi are grown m culture 

 media, is much more pronounced when the mycelium grows in the cortex, and 

 that we have here proof of the advantages which the Ericaceae derive from this 

 association. The author's cultures show that the infection may be Jra^smitted 

 through the seeds and does not come necessarily from the soil. 



Development of leaves.-LEWis'« has published a second study of leaf develop- 

 ment, in which he shows "that the basipetal and basifugal directions of growth 

 may both occur in a single leaf; and that, although one becomes Fedommant 

 evidences of the other are apparent." In a previous paper" he ^'"^ J^ 

 question whether certain forms of adult leaves could be due to arrested develop- 

 ment, "so that by comparing the mature leaves of a given plant something o theur 

 embrj-ological history could be learned." The general conclusion is ^^t 'e^^^^ 

 of very diverse species show a common method of leaf development, in which the 

 basipetal and basifugal directions of growth are combined; and by he preu 

 nance of the basipetal or the basifugal elements, palmate or P'^^^^e jeav^" e 

 produced respectively. The author thinks that there is shown a ^^^^^l 

 evolution of leaf forms, whereby diverse species tend to produce ^i-^^J^^^^^^^ 

 Plants with simple le'aves constantly show tendencies '^l'^J^X^'^< 

 "Thp r^..;.,^^, l..i„.t,-^. of the similar forms of compound leaves wmtu 



determinate 



J.M 



^Pt^^.z, Charlotte, Ueber die Assimilation des atmospharischen Stickstoffes 



durchPilze. Jahrb. Wiss. Bot. 44:353-4o8. 1907- AmerXat. 41: 



^^ Lewis, FREDERIC T., A further study of leaf development. Amer. - 



701-709. 1907. 



^7 Amer. Nat. 41:431-441- 1907- 



