Lecture 5 — 117 — Artificial Media 



absorption, as tested by bromide ions, but the intact 

 plants did not react alike. Rice plants can absorb 

 salt and grow satisfactorily when the roots are placed 

 in an anaerobic or nearly anaerobic environment. The 

 conclusion seems to be that necessary oxygen required 

 by the roots of the rice plant can be translocated 

 from the shoot.* To a somewhat lesser degree this 

 would be true of the barley plant. According to the 

 studies of Vlamis, a high rate of aeration of the cul- 

 ture medium, while it may temporarily accelerate salt 

 absorption by the rice plant, soon produces injured 

 root tips. 



Another factor to be taken into account in a dis- 

 cussion of nutrient solutions or other root media is 

 that of temperature. It was mentioned in a previous 

 lecture that short period studies on the absorption 

 and accumulation of inorganic solutes by excised roots 

 of barley plants, or by intact plants, disclose a high 

 temperature coefficient for this process, within certain 

 ranges of temperature. In longer time periods the 

 temperature question becomes much more complex, 

 since the whole plant system is undergoing change 

 and development. Furthermore, rates of movement of 

 solutes from the root to the top of the plant and of 

 the transport to the root of carbohydrate or of growth 

 substances must also govern the activities of roots 

 and the absorption and upward transport of solutes, 

 as I have already attempted to show. There seems 

 to be comparatively little evidence on record of root 

 temperature effects on plant growth from experiments 

 conducted under controlled conditions by water-culture 

 technique. A series of systematic studies has there- 

 fore been initiated on crop plants of different species 

 to be grown under the aerial environment of a green- 

 house at different seasons, with the nutrient solutions 



*There is some evidence that plants of this character 

 possess anatomical adaptations facilitating the internal aeration 

 of roots. 



