SCHREINER AND REED: EXCRETIONS BY ROOTS 287 
presence of excreta from plants of the same and other species. 
The latter experiments employed seedlings of corn (Zea Mays), 
cowpeas (Vigna Catjang) and oats (Avena sativa). 
For the purpose of making investigations upon the chemotro- 
pic behavior of roots it was necessary to employ a medium which 
was as nearly non-nutrient as possiblee In the first experiments 
clean quartz sand was used as a medium in which to grow the 
plants. Owing to the difficulty of filling the tubes of small dia- 
meter and the necessity (described below) of rotating the cultures, 
the sand was not suited to the purpose of experimentation. After 
some preliminary tests, agar agar proved to be a very satisfactory 
medium to serve as a substratum. The fibers of agar agar were 
soaked in one or two changes of distilled water at room temper- 
ature to remove the slight amount of soluble matter present. The 
agar agar was then melted by boiling it in distilled water in the 
ratio of 2 parts of agar to 100 of water. The melted agar was 
filtered through absorbent cotton and gave a preparation which 
remained clear when reheated. The agar was poured out and 
allowed to cool to 30°—35° C. at which temperature it was just 
beginning to harden. The roots of the seedlings were put in at 
this time and were firmly held when the agar became set. In agar 
Prepared in this manner the root system developed in a perfectly 
Normal manner. The roots were clean and white, and showed no 
distortion nor swellings as they do in unfavorable media. The 
behavior of the roots could be noted at any time through the 
transparent agar jelly. The glass receptacles in which the seed- 
lings grew were always covered with black paper to exclude light. 
Since the agar jelly contained about 98 per cent. of water, the 
Plants were able to obtain an ample supply for growth. Small 
quantities of distilled water were added daily to keep the surface 
Of the agar moist and to prevent the formation of fissures. 
The remarkable freedom of the agar from growth of moulds 
and bacteria showed how free it was from substances which might 
Serve as nutrients. Although the jars containing the agar cul- 
tures stood open from 4 to 10 days they were very rarely infested 
With moulds or bacteria and the few plants that were thus infested 
Were discarded * from the results. 
* Vide infra for experiments eliminating bacteria, 
