328 



SCIENCE 



[N. S. Vol. XLIII. No. 1105 



was a fixation or increase in nitrogen over that re- 

 moved from the soil. When grown in association 

 there was a loss of total nitrogen with the follow- 

 ing combinations: barley and peas, rye and vetch, 

 rye and peas, rye and clover, Kafir corn and peas, 

 Kafir corn and clover, corn and millet, and corn 

 and oats. There was an increase in nitrogen with 

 the following combinations: barley and vetch, bar- 

 ley and clover, oats and vetch, oats and peas, oats 

 and clover and Kafir corn and vetch. 



The quantities of nitrate nitrogen remaining in 

 the son were comparatively low after harvesting 

 millet, corn, Kafij corn and beets; and somewhat 

 higher after clover, vetch, soy beans and peas; and 

 still somewhat higher after oats, wheat, barley and 

 rye. 



A Physiological Study of Certain Strains of Fusa- 

 rium oxysporum and Fusarium trichothecioides 

 in their Causal Eelation to Tuber-rot and Wilt 

 of Solanum tuberosum: Geo. K. K. Link. 

 Certain strains of Fusarium oxysporum and 

 Fusarium trichothecioides can produce both tuber- 

 rot and wilt of the Irish potato. The wilt is in- 

 duced by destruction of the root system and by 

 clogging of the xylem elements in the stem and is, 

 in mild cases, marked by such symptoms as dis- 

 coloration of leaves, curling and rolling of leaves, 

 and production of aerial tubers. Under field and 

 storage conditions Fusarium oxysporum is prob- 

 ably more responsible for wilt than is Fusarium 

 trioothecioides, and Fusarium trichothecioides the 

 more responsible for tuber-rotting. This may be 

 explained in part by the fact that the optimum 

 and maximum temperatures of Fusarium oxy- 

 sporum are higher than those of Fusarium tri- 

 chothecioides. Fusarium trichothecioides, how- 

 ever grows well at S'-IO" C, while Fusarium oxy- 

 sporum does not. Fusarium oxysporum also has a 

 more rapid, superficial and spreading habit of 

 growth than has Fusarium trichothecioides. Both 

 organisms possess a truly striking cosmopolitan 

 ability to use the most diverse carbon materials as 

 carbon sources in their metabolism. Fusarium 

 oxysporum, however, is more cosmopolitan in its 

 ability, and can utilize materials more readily than, 

 though not so completely as, does Fusarium tri- 

 chothecioides. Fusarium oxysporum also is less 

 subject to inhibition in growth and intoxication 

 than is Fusarium trichothecioides. 



Some Factors Determining the Presence of Fat as 

 a Food Beserve in Woody Plants: Edmund W. 



SiNNOTT. 



Reserve fat occurs most abundantly in those 

 woods where the rays and parenchyma cells are 

 comparatively thin-walled and well provided with 

 pits, and is particularly well developed in the cells 

 immediately adjacent to the vessels. It is prac- 

 tically absent in species with thick-walled, slightly 

 pitted parenchymatous tissue. These facts sug- 

 gest that the occurrence of fat in wood and its 

 distribution there may depend on the ease of dif- 

 fusion of some fat-forming ferment from the 

 vessels through the rays and parenchyma. Ex- 

 periment shows the presence of a fat-splitting fer- 

 ment in the leaves and bark, which varies greatly 

 in amount according to species and season, but 

 which is in general most abundant in the spring 

 in those species where reserve fat was most 

 abundant in winter. It is suggested that perhaps 

 this fat-splitting ferment (lipase) may here be re- 

 versible in its action and that during the late 

 summer and fall it may be diffused downward 

 through the wood and bast, converting into fat the 

 food reserves to which it has access. 



The Influence of the Medium upon the Orientation 

 of Primary Boots: Eichaed M. Holman. 

 In this paper were considered the explanations 

 offered by Hofmeister, Sachs, Elfving and NemeC 

 for the difference in behavior of primary roots 

 growing in air and in earth when displaced 

 from the normal perpendicular position. The au- 

 thor's experiment indicates that the failure of 

 roots in air to bend downward after the autotropic 

 flattening of the primary geotropic curvature is 

 not due to absence of contact stimulus as Sachs 

 suggested, nor to a change in the geotonus of the 

 root as Nemefi's results seem to indicate. By the 

 use of media whose resistance to penetration by 

 the root tip could be widely varied, roots were 

 caused to behave very nearly as in air or in the 

 same manner as in earth, according as the medium 

 was loose or considerably compressed. The au- 

 thors' experiments indicate that the effect of the 

 medium is primarily if not exclusively mechanical. 

 The resistance offered by the medium to the ad- 

 vance of the downward curved tip of a root which 

 has flattened its primary curvature tends to pas- 

 sively depress the root and in this manner the root 

 is enabled to complete the geotropic reaction in 

 media which offer appreciable resistance to the 

 advance of the tip. Vicia faba, Lupinus albus 

 and Pisum sativum were the principal species em- 

 ployed, although many other forms behaved simi- 

 larly. Secondary roots of the three species men- 



