470 BROOKLYN BOTANIC GARDEN MEMOIRS 



which followed was due to the excelsior alone. All of the plants were 

 in the seedling stage and the duration of the experiments in no case 

 exceeded fifteen days. The investigations relating to contact stimu- 

 lation of roots were limited to the use of a few species which show 

 different types of reaction. The results of these experiments are 

 shown in Tables 16-18, although several other species were employed 

 which are not included here. In all cases, the "excelsior coarse" 

 implied the loose commercial form which came in contact with roots 

 occasionally, while "excelsior fine" was in these particular experiments, 

 cut up into lengths 4 cm. long and furnished considerable contact. 

 When such plants as lupines and peas which possess strong and fairly 

 good-sized primary roots were in contact with excelsior the reaction 

 was characterized mainly by an accelerated growth of the primary 

 root system, together with considerable secondary root development 

 whereas in the case of delicate roots, such as mustard (Table 18 ), the 

 growth of the primary roots is less and the secondary root development 

 is greatly accelerated. Practically little or no difference existed in 

 the growth of hypocotyls and stems in any case, although this feature 

 is not always constant. In both the lupines and peas (Tables 16 and 

 17) there occurred a considerable accelerated growth of the primary 

 roots. In the latter case (Table 17), which represents an average of 

 four experiments, there was a decided increase in the number and 

 length of secondary roots from the normal to the fine excelsior. In 

 one experiment where the secondary roots were counted, their average 

 number was as follows: 



Normal 17 



Coarse excelsior 32 



Fine excelsior 40 



This feature was more pronounced in the mustard, however, where 

 the primary roots in contact with the excelsior were much less de- 



Table 18 



Showing Growth of Hypocotyls and Roots of Mustard {Brassica alba Boiss.) in Water 



Containing Excelsior^^ 



Average Length of Hypocotyls and 

 Primary Roots (Centimeters) 

 Treatment Hypocotyls Roots 



Normal 12. i 11. 1 



Excelsior coarse 13.3 6.8 



Excelsior fine 11.9 8.9 



veloped (Table 18). In this case there were no secondary roots on 

 the normal plants; many in the coarse excelsior and very numerous 



^^ 20 plants used in each test. 



