NOTES ON ROOT-HAIRS AND ROOT GROWTH. 
179 
Glance to the warty outgrowths met with on the leaves of vines, 
and which I have lately seen on the foliage of forced potatos, 
and they call to mind the spongy investment of the aerial 
roots of Orchids and Arads, and the similar hut firmer 
.growths which invest the roots of Cycads when they are 
thrust up above ground. These points seem all significant, 
but, for want of fuller information, I pass them by with 
the mere mention, and proceed to narrate the details of 
some experiments made with a view of obtaining informa¬ 
tion as to the production of root-hairs. 
The experiments were carried out in the following manner :— 
Seeds of Mustard ( Sinapis alba ), and of Cress (Lepidium sativum) 
were sown on the same day in 6-in. (top diameter) flower pots, 
£lled with soils of various characters, thus :— 
(1.) Two pots were filled with stiff yellow clay, rammed in 
hard. 
(2.) Two with washed gravel pebbles, varying in size from 
that of a pea to that of a hazel nut. 
(8.) Two with lumps of “ballast” or burnt clay, varying 
in size from the dimensions of a filbert to those of 
a walnut. 
(4.) Two with rich garden mould. 
(5.) Two with layers of flannel. 
(6.) Two with compact layers of half-rotten leaves. 
(7.) Two with road scrapings. 
These substances were chosen as affording varying degrees 
of permeability; thus, Nos. 1 and 6 were likely to be penetrated 
with difficulty by the radicles; Nos. 2, 3, and 7 might be 
expected to be readily, and Nos. 4 and 5 moderately, traversed 
by the roots. The capacities for holding water, admitting air, 
and of furnishing nourishment may also be presumed to have 
varied in each case. 
The seeds were chosen by reason of their ready and speedy 
germinating power, and because while the Mustard produces 
a large quantity of root-hairs, the Cress produces, under the 
same circumstances, so few, that a lens is usually requisite 
to see them at all. 
The seeds were sown on the 22nd of January, 1878, one 
half of each pot being occupied with Mustard,] the other half 
