472 BROOKLYN BOTANIC GARDEN MEMOIRS 
The normal or check series were run in water alone. The results 
given by these experiments, which were limited in numbers, are 
similar to those obtained by the use of excelsior in contact with roots 
in water, namely, the various grades of gravel, sand, and silt gave 
rise to different reactions on the part of the organism which resulted 
in a stimulated growth correlation, as exemplified in the development 
of the primary organs and secondary root system. The results ob- 
tained by the use of mustard, peas and soy beans, etc., in the experi- 
ments so far carried on, indicate generally that there exists little 
difference in the height of the hypocotyls or stems of the normals, 
and those in contact with the different-sized particles of soil constit- 
uents. The growth in length of the primary root is lessened and the 
secondary root system is greatly increased as we approach the finer 
grades of contact material. In some species with relatively large 
roots the coarser particles, namely 16-8 mm., appear occasionally to 
stimulate primary organs, but this reaction is variable, and associated 
with growth correlations as manifested in the more or less increased 
development of the secondary root system. The reaction of roots 
to different-sized particles will undoubtedly be found quite variable. 
Species with relatively large and strong primary roots such as the horse 
bean, peas, etc., react differently from seedlings with a delicate root 
system, such as the mustard and turnip. The roots of the latter 
species, even when grown in contact with excelsior or soil particles, 
produce a marked secondary root system characterized by little or 
TABLE 19 
Showing Growth of Hypocotyls and Roots of Mustard (Brassica alba Boiss.) in Contact 
with Different-sized Particles of Sand and Gravel in Water'® 
Average Length of Hypocotyls and 
Primary Roots (Centimeters) 
Size of Particles 
(Millimeters) Hypocotyls Roots 
INormal eee eat Soo 8.7 1247 
TO—Sieees Peas eo ee oes eioe 8.2 12.6 
SoA ret goer et Aes Rade ite) 8.7 
Baoan Rar rcesuaie ence see ema ener 11.5 7.6 
2 TARAS See SAR eRe AG EN 11.9 4-4 
DONS ties Sele ane Cee eee 11.6 4-3 
OF5=O0 25a eer cee ele TL:2 4.2 
OP25 SO 81t ere ten aeereteat forte 1257, 3.4 
no primary root development. The same tendency exists in species 
characterized by larger roots to increase their secondary root system. 
On the other hand, the primary root system is greatly accelerated by 
contact with excelsior in species with large roots. (Cf. Tables 16-17 
and 18.) The experiments with mustard given in Table 19 show 
19 75 plants used in each test. 
