60 PHYSIOLOGY [BoT. Absts., Vol. VII, 



water-proofing effect of resin — especially above 50 per cent humidity. The germination curve 

 for spores of Lenzites saepiaria illustrates the fact that spore germination is greatly accel- 

 erated when the atmospheric humidity is high enough to maintain fiber saturation of the 

 wood. — A humidor for maintaining constant humidity and temperature is described. It is 

 provided with a dew-point apparatus for the determination of humidity, and a weighing 

 device by means of which the samples can be weighed without opening the humidity chamber. 

 —S. M. Zeller. 



MINERAL NUTRIENTS 



401. BoTTOMLEY, W. B. The growth of Lemna plants in mineral solutions and in their 

 natural medium. Ann. Botany 34:345-352. 1920. — Lemna major and Lemna yninor cannot 

 grow normally in Knop's or Detmer's solution, but the addition of certain organic substances 

 to these solutions permits rapid and healthy growth. These organic substances essential 

 to the metabolism of the plants are to be found in the w^ater of the ponds in which the plants 

 normally grow, and maintain the plants in health, although lack of sufficient quantities of 

 nitrates and phosphates under these conditions acts as a limiting factor, retarding their rate 

 of multiplication. — G. M. Armstrong. 



402. DuGGAR, B. jNL Hydrogen ion concentration and the composifcion of nutrient solutions 

 in relation to the grov/th of seed plants. Ann. Missouri Bot. Card. 7: 1-50. 7 fig. 1920. - 

 For several years the author has been examining the effect of the reaction of the medium 

 on growth in certain physiologically balanced nutrient solutions and has secured many data 

 concerning the extent of change of the Ph value of the solution in which the plants have 

 grown, as well as concerning growth relations with the variations in active acidity. Thus in 

 this report of experimental work particular reference is not made to the proportions of the 

 different salts involved in the nutrient solutions except as they may influence the active 

 acidity. For this report four solutions were used, as follows: Solution A was a slight modi- 

 fication of Shive's solution, having the following partial volume-molecular proportions — 

 KH2PO4, 0.0180; Ca(N03)2, 0.0052; MgS04, 0.0150; and "soluble ferric phosphate," 0.0044 

 gm. per liter. Solution B was an extreme modification of the Crone solution, having the 

 following proportions of salts— KNO.,, 0.00495; CaS04, 0.000726; MgSO,, 0.000526; and "sol- 

 uble iron phosphate," 0.125 gm. per liter; this is a four-salt solution having a higher pro- 

 portion of iron than the usual nutrient solution. Solution C was the Livingston and Tot- 

 tingham solution, modified by the addition of "soluble ferric phosphate" as in Solution A— 

 KNO,, 0.0216; CaCHzPOJj, 0.0026; and MgSO,, 0.0150. It is assumed that the osmotic 

 value of solutions A and C is approximately that of Shive's solution — 1.75 atmospheres — 

 while that of Solution B is much less. — The culture methods employed were essentially those 

 described before. Seedlings of corn, field peas, and vv^heat were used. For the determination 

 of active acidity the standard solutions and indicators suggested by Clark and Lubs were 

 emploj'ed. The total green weight with the remains of the seed, or cotyledons, cut away 

 was used as an index to growth. In this way the health and growth of the plant is most 

 favorably expressed. — The experiments were conducted under a considerable range of environ- 

 mental conditions. "Under the most favorable conditions, the three solutions mentioned 

 above, without other modifications, may all yield excellent growth. Plants grown in Solu- 

 tion B are invariably a deeper green, presenting a finer appearance and the average of the 

 growth quantities is higher for wheat and corn than in either of the other two solutions. In 

 the unmodified Solutions A and C, the green weight of peas averages higher than in the 

 unmodified Solution B." Solutions A and C contain a monobasic phosphate and should 

 have a Ph value of about 4.5. Experience shows that Solution B varies in active acidity 

 from Ph 5.4 to Ph 7.1; although it is frequently 6.6 to 7.1. "Culture solutions prepared with 

 monobasic phosphates may, however, exhibit a hydrogen-ion concentration which is too 

 high for .... best growth under certain conditions, and especially is this true in the 

 case of wheat." Solutions made with monobasic potassium or calcium phosphate, unless 

 previously purified, may yield a Ph which is distinctly toxic. Correction to Ph 4.8 to 5.2 by 

 means of NaOH or by use, in part, of a dibasic salt generally yields better growth. Under 



