4io Hill. — The Morphology and Seedling Structure of the 
Longitudinal sections through young and old tubers show this peculiar 
unilateral development in a very striking manner. The course of the stele 
in the hypocotyl of the seedling is at first vertical (cf. Fig. 34, PL XXX) ; this 
then becomes curved, being pushed aside by the stronger development of 
cortical tissue on one side of the hypocotyl, until it forms a semicircular 
loop at the upper end of the young tuber, uniting the now contiguous 
points of egress of stem and root. The main mass of the tuber is situated 
below this stelar loop, and consists of parenchymatous tissue stored with 
starch ; the tuber is bounded by a cuticle, but there is no development of 
any corky tissue (Fig. 40, PL XXX). 
The tuber never seems to attain to any large size ; the largest seen are 
about 5 mm. in transverse diameter by 3 mm. in height, of a yellow colour, 
and often have a wrinkled skin. Since we have no precise information as 
to the nature of the habitats of the species which possess this type of 
tuber, or of the particular conditions under which they grow, it may not be 
very profitable to speculate on the possible reasons for this peculiar 
adaptation. The roots running horizontally above the tuber show that 
their object is to be close to the surface of the soil, and this would suggest 
that the need of oxygen may have stimulated them to grow in this manner. 
This view Is strengthened on recognizing the definitely apogeotropic nature 
of the first lateral root of the young seedling (Figs. 33 and 34). 
The leaf petioles in P. pedicellata, Dahlst., are some 6 to 7 cm. long, and 
bear cordate-peltate acute laminae, some 2*5 to 3 cm. long by about 2 cm. 
broad (Fig. 32, PL XXX). Owing to the small size of the tuber, it seems 
probable that the plants are able to grow actively with the help of their leaves 
and roots during the damp season, and are not dependent on the store of 
nutriment in their tubers. During the dry season or on the incidence of 
an unfavourable time this organ may be of great value to the plant, both 
in preserving its life and in affording a supply of nutriment for the 
resumption of active growth on the recurrence of favourable conditions. 
The texture of the lamina in the dry specimen is membranous and 
thin, like that of P. peruviana, and is in marked contrast to the small thick 
lamina of P. parvifolia and its allied species. This character suggests that 
the habitat of the species is damp and shaded, at least during the vegetative 
period, and the position of the roots is also suggestive of a wet situation 1 . 
Other Bulbous Species. 
P. umbilicata, H. B. and K. 2 , is a much larger and stouter plant than 
P. pedicellata, having fairly large orbicular and medianly peltate leaves, 
which are firm in texture and possess clearly marked veins. The tuber is 
1 It is of interest to notice that P. peruviana , which bears its horizontally running roots on 
the sides of its tubers, also grows in damp and shady places. 
2 H. B. and K., 1. c., i, p. 59, Taf. xv, Fig. 1. 
