78 TRANSACTIONS OF THE [Sess. i-xxx 



thickness of the walls of the sclerosed ground tissue and 

 of the cells of the " multiple endodermis." The extent of 

 thickening in both cases is progressively less, as in the 

 order stated — 



(1) Aerial. 



(2) Damp soil. 



(3) Gravel. 



(4) Water ) 



(5) Soil r™'" 



In the cortex of the water-culture roots lacunae are 

 found. Freidenfelt in " Der anatomische Bau der Wurzel," 

 Bibliotheca Bot., 1904, p. 75, shows that an increase in the 

 water content of the soil decreases the number of hairs 

 found on the root. The piliferous layers of the roots 

 cultivated in the different media vary. Aerial, soil, and 

 gravel roots have practically the same quantity of hairs, 

 but the respective average lengths are 1'25 mm., I'lo mm., 

 1-08 mm. The hairs of the water roots are more numerous, 

 but they are short, the average length being -47 mm. The 

 piliferous layer of the damp-soil roots is feebly developed, 

 and the average lengtli of the hair is '5 mm. 



Summary. 



1. The development of the absorptive layer varies 

 inversely with the humidity of the medium. 



2. Tlie development of the mechanical tissue varies 

 directly with the humidity of the medium. 



3. There is no variation, as one would expect, in the size 

 of the intercellular spaces of the fundamental tissue, 

 excepting the presence of lacunae in the cortex of the 

 water roots. 



EXPLANATION OF PLATE. 

 Monstera deliciosa. 

 Fig. 1. T. S. rout (jrovm in vxUer. 



(a) Multiple endodermis. 



(b) Sclerosed ground tissue. 



(c) Fibrous hair. 



(d) Lacuna. 



Fig. 2. T. S. (lervd root. 

 Letters as in fi''. 1. 



