•54 
62. COXVOLVULACEiE. 
thickly in shallow trenches, on a layer of manure, the long 
trailing branches or runners (ramos) of the pi. The roots of 
these produce tubers fit for digging up in from 3 or 4 to 10 or 
12 months. The best Batatas are produced in a light dry fri- 
able and well-drained, not over moist close soil. 
The value of the Demerara sort consists in its more abundant 
yield and speedy production of tubers, allowing 3 or even 
sometimes 4 crops to be raised in lieu of one of the old sort. 
Thus on the destruction of the Potato-crops in 1845-6 by the 
then prevalent disease, its simultaneous accidental introduction 
from Demerara into the island proved a most providential alle- 
viation to the famine and distress (see Journ. Ilort. Soc. i. 
177). 
I have endeavoured in vain to find any stable characters to 
separate further the 2 sorts or varr. above distinguished. The 
1. in the old sort (3 are smaller darker lurid smoky gr., the st. 
perhaps more often suffrutescent downwards, and the fl. seem 
more closely aggregate or clustered in the cymes. The newer 
Demerara sort a is also on the whole a stouter stronger more 
robust luxuriant pi. with mostly light or pure full gr. foliage-. 
I have been unable to detect any difference in the st., foliage 
or fl. corresponding regularly with that of the shape or col. of 
the root-tubers, in either of the kinds. 
The tubers are usually about the size of Potatoes ; but I once 
(May 1861) saw several from Grand Canary weighing 6-71 lbs. 
each ; and I have heard of one in Mad. at Machico said to have 
weighed an Arroba (32 lbs.) ! after having been left in the 
ground 2 or 3 years. Nor indeed is this enormous size at all 
incredible for a pi. allowed to grow several years undisturbed. 
ff3. Pharbitis Chois. 
ftl. P- PURPUREA (L.). 
St. elongate twining, retrorsally hispid; I. cordate acute or 
subacuminate pubescent or glabrescent stalked ; ped. 2-3-fld. 
shorter than the 1. ; pedic. umbellate hispid upwards, thickened 
and stiffly cernuous m fr. ; sep. thickly hairy almost hirsute at 
the base, smooth upwards, ovato-lanceolate or lanceolate ; cor. 
large v.-blue, p. or w. with 5 equidistant darker rays or streaks. 
Vonvo/r. purpurea* Linn. Sp. 210; MM, It. 113, 1005, 1082; 
Ait. Hort. Kew. (ed. 2) i. 330; Spr. Syst. i. 697. Ipomcca 
