152 



MASS. EXPERIMENT STATION BULLETIN 277 



did have a soil temperature considerably higher than that of a porous pot. 

 However, no experimental evidence could be obtained wliich would indicate 

 anyeflfect on plant growth. Tomato plants in clay, paper, and glass containers 

 grown in a night air temperature of 80° F. were larger than a similar series 

 grown at a temperature of 60° F., but the relative differences between the 

 plants in the various containers in the same series remained the same. Fur- 

 tliermore, the soil temperature in the paper pot was more like that of the 

 glass containers, yet plants in the glass containers were frequently better 

 than those in clay pots and the plants in the paper pots were poorer than 

 those in the clay pots. These results indicate that the soil-temperature factor 

 is as unimportant as the porosity factor so far as it applies to growth in 

 paper pots. 



The habit of growth in the paraffined paper pots was quite similar tj 

 growth obtained when a nutrient deficiency exists. The leaves of the plant 

 turned to a yellow green and became stiff. New leaves grew slowly and re- 

 mained small. These plants resembled plants that have been exposed to very 

 cool temperatures or have been put on a ration of a reduced quantity of 

 water. These practices, i. e., cool temperature and little water, are used in 

 the method of "hardening-off" plants either to hold them back in growth or 

 to prepare them for the more rigorous life of field culture. However, the root 

 system was very much unlike the strong root systems of j^lants that have been 

 hardened-off. The ball of roots witli soil was not present. The roots were 

 very few and showed little tendency to branch. This absence of a fibrous root 

 system on the outside of the soil mass was not due to lack of moisture on 

 the outside of the potted soil. The paper pot soon became quite moist and 

 in many cases was penetrated by roots that were working downward on the 

 outside of the pot. Numbers 11 and 12 in Figure 1 show the poor root systems 

 of plants grown in plain paper and paraffined paper pots. Numbers 16 and 

 17 are plants grown in clay and glass containers, showing excellent root 

 svstems. 



3 'Im 



Fig. 1. — Calendula Plants, 40 days in 4-inch containers. 



No. 11, plain paper pot; 12, paraffined paper pot; 13, 14, 15, BakeUte varnishes 

 on paper pots; 16, clay; 17, pint size glass fruit jar. 



The leaves of the plants were strikingly similar to leaves on plants suf- 

 fering from a lack of available nitrogen. Tomato plants in clay and paper 

 pots were given an application of an aiiuuonium sulfate solution (1 ounce to 

 1 gallon) when the plants in the i)aper ])()ts had apjjarcntly stoj)ped growing. 



