218 
Hill. — Studies in Seed Germination. 
M. horridus. — The species whose germination has been most carefully 
studied is M. horridus , Dunn, seeds of which were collected in the Kaweah 
River Valley, California, at 6,000 ft., by Mr. F. R. S. Balfour. Of the 
region it inhabits, Mr. Balfour writes: ‘ The district for five or six months 
of the year is under very deep snow, but from May to October there is 
cloudless sunshine without a drop of rain.’ Nothing is known of the 
germination of the seed under natural conditions, but it is probable that 
the seed remains buried under the snow, and may be carried into the 
ground during the winter, germination taking place in the late spring. 
Judging from observations made under greenhouse conditions, germination 
when started would proceed rapidly, and the plumular shoot would no 
doubt soon appear above ground. This shoot, however, in its first year 
would probably only have a comparatively short existence. 
The seeds in M. horridus are ovoid with a thick testa, and measure 
about 3 75 cm. long. At the broad end they are about 1 cm. in diameter 
across the cotyledons, and at the narrow end towards the apex the dia- 
meter is about i*8 cm. The cotyledons are thick and fleshy, somewhat 
hollowed and fused together at the base. Each cotyledon is about 4 mm. 
thick, and is stored with aleurone and oil. 
On germination, the testa bursts by a longitudinal fissure commencing 
at the micropyle and gradually extending along the pronounced ridge 
encircling the seed, until by the swelling of the cotyledons it is split into 
two portions. The petiolar tube carrying the plumule and radicle at its 
apex quickly elongates and bends over, growing vertically downwards into 
the soil (PL V, Fig. 3). The tube is covered with a mat of fine, some- 
what woolly, unicellular hairs, to which particles of soil adhere after the 
manner of root-hairs ; these hairs in fact, until the radicle develops from 
the end of the petiolar tube, apparently perform the function of root- 
hairs and absorb the moisture required for the development of the embryo 
(Figs. 3-7). 
The tip of the petiolar tube ends abruptly, in the early stages of 
germination, in a short brown conical tip which is surrounded by a loose 
and more or less detached flange or root-cap. The flange may in part 
represent some portion of the inner seed-coat carried away by the tip 
of the petiolar tube, and is also no doubt part of the cap of the radicle 
itself whose tip forms the actual apex of the cotyledonary tube (PL V, 
Figs. 3, 4, and 6). While the petioles are elongating and carrying the 
plumule and radicle into the ground, very little development of either 
organ takes place (Fig. 5), but after an appropriate depth has been reached 
the radicle begins to elongate, develops root-hairs, and quickly grows down 
into the soil and sends out lateral roots, anchoring the plumule firmly 
in the ground (PL V, Fig. 7). 
About this time a slight swelling becomes noticeable at the point 
