loO MASS. EXPERIMENT STATION BULLETIN 277 



M)t has a cooling effect on the soil. Experiments conducted by Jones (7) 

 ,how that a difference of 20° F. may exist between the soil temperatures of 

 i clay pot and a non-porous pot, the clay pot being- tlie cooler. By weighing 

 cxt fre(juent intervals, it was found that twice as nuich water was lost from 

 the porous pot as from the non-porous pot. In Table 2 is shown the loss of 

 weight from porous and non-porous three-inch flower pots and the tcmiier- 

 ature at the center of the soil mass. As the surface areas of the two types 

 of pots were the same, the greater moisture loss in tiie porous pots was due 

 to the evaporation from the outside surface of the pot itself. This double 

 loss of moisture from the porous pots was again checked in a later phase of 

 the investigation which brought out the fact that the porous pots required 

 twice as much attention for watering as did the non-porous pots. 



Table 2. — The loss of moisture from porous and kon-porous pots and the 

 effect of evaporation on soil temperature in these containers. 



TOTAL 38.6 42.0 16.1 15.9 



However, there has been no indication that the excessive evaporation from 

 the porous pots affects the growth of the plant from the temperature angle. 

 There is sufficient evidence to state that the excessive evaporation ultimately 

 leads to a water deficit in a portion of the soil and that this deficit is not 

 made up by the daily practice of watering. 



If, however, the tin can or some other non-porous container is used, there 

 can be no adsorption of moisture by the container and hence no evaporation 

 on the outside surface. All the water applied is evenly distributed and kept 

 in balance throughout the soil mass. The range of moisture content is nuic'.i 

 smaller than in the porous container and tlie response by the })lant is con- 

 sequently a steady growth, if temperature and light are suited to the ])lant. 



If ])orous containers are to be used in rooms where the relative humidity 

 is low, it is advisable to keep such containers on a moi.st surface. This is 

 best secured by resting them on a shallow mass of moi.st sphagnum moss, 

 such as is used by florists for making funeral set pieces. The porous pot will 

 continue to evaporate its moisture, but will replenish the loss by taking up 

 the moisture from the moss. Standing porous pots in free water may be 

 practised, but this method may lead to a water-soaked soil and consequent 

 lack of aeration in the soil. 



Paper Flower Pots 



Paper flower pots may be successfully employed for growing ))lants, if 

 the paper is properly impregnated with a substance that will prevent the de- 



