1921] HOWE—ROOT HAIRS 3t7 
It was also more difficult to find the young root hairs on the roots 
grown in sand. Pectic material was found in the outer layer of all 
the root hairs; some of it was in the form of calcium pectate in 
practically all the root hairs, much was in the form of pectose, and 
it was difficult to determine with certainty whether some was in the 
form of pectic acid. By the application of 2 per cent hydrochloric 
acid the pectose was changed to pectic acid except in a few instances 
when some was changed to pectin, and the calcium pectate was 
broken down to calcium chloride, allowing pectic acid to be set 
free. Why pectose is changed sometimes to one form and some- 
times to the other is still an unsolved problem. 
Callose forming an inner lamella of the wall was found in all 
the root hairs, being somewhat thicker at the tip, especially of the 
younger root hairs. The hairs grown in the two media did not 
differ essentially in these respects, except that ‘the callose was 
somewhat thicker at the tips in loam than in sand. No cellulose 
was found in the root hair walls. As the root epidermal cell 
bulges to form a hair, the cellulose inner lamella apparently stretches 
to its capacity, then breaks, and no more cellulose is formed. It 
may be that under other conditions more cellulose would be formed. 
‘The root hairs gave an acid reaction in all cases both in the 
loam and in the sand, but usually somewhat higher in the loam 
than in the sand. According to the P,, value, they ranged between 
6.8-6.0 in the sand and in the loam, and in some cases in loam 
between 6.0-5.2. 
The seedlings of only four species were grown in Knop’s solution, 
and the hairs were quite numerous and symmetrical. Before the 
seeds were placed for germination in the Knop’s solution, it was 
tested and found to have an acidity of 6.8-6.0. After the seedlings 
had grown, both the root hairs and the solution were tested for 
acidity. The root hairs showed about the same degree of acidity or 
a little less than that of the root hairs grown in the soil, while the 
solution was also less acid than the original, even becoming alkaline 
in three of the cases. These root hairs had the same structure as 
those grown in loam and sand, except that the callose was thicker 
at the tips and in two of the cases the pectose was changed to 
pectin 
