Hill. — Studies in Seed Germination. 
2 1 7 
of the metabolic activity of the plumule and radicle, and eventually assumes 
very large proportions. 
Darwin describes the occurrence of absorbent hairs on the petiolar 
tube of Megarrhiza californica , and they have been noticed in all those 
species with a well-developed cotyledonary tube, but in Marah fabaceus no 
such absorbent hairs are present. This is no doubt due to the shortness of 
the tube and to the rapidity with which the root bearing its own root-hairs 
develops. Except for the fact that the petioles of the cotyledons are fused 
to form a short tube, the type of germination exhibited by this species may 
be compared with that of Aesculus, where a certain elongation of the 
cotyledonary petioles takes place to carry the radicle and plumule out 
of the seed. 
M. micranthus and M. macrocarpus. — The germination of the seeds 
of M. muricatus , Greene, and M. micranthus , Dunn, is so similar to that 
of M. macrocarpus (M egarrhiza californica ) that there is little to add to 
Darwin’s account. 
In M. micranthus and M. macrocarpus the seeds are orbicular or ovoid, 
•about i*5 cm. long by 6 to 8 mm. broad, and the cotyledons are united 
towards the base. The petiolar tube in M. micranthus reached a length 
of 2 to 3 cm., and split for some distance on the emergence of the plumule. 
The hypocotyledonary tuber was ovoid, and quickly emitted roots. 
In M. macrocarpus the petiole tube grows as much as 6 cm. vertically 
into the ground, and it is probable that in its native home it may attain 
a greater length and carry the plumule deep into the soil as a protection 
against drought (PI. V, Fig. 9), 
Under artificial greenhouse conditions the plumule bursts through the 
tube soon after the root has become well established, but under natural 
conditions it is probable that there may be a considerable resting period 
after the plumule has been safely deposited deep down in the earth, whilst 
the tuber is developed at the expense of the reserves .stored in the seed, and 
until conditions become favourable for the development of the climbing 
shoot. 
M. muricatus. — A number of seeds of M. muricatus were received 
from California, but only one germinated. In this species, the seed is 
flattened and somewhat orbicular-rhomboid in outline, i*8 to 2*o cm. in 
diameter. The cotyledons are only 1 to 2 mm. thick, and free except, as 
in other species, near the base, where they are definitely fused together. 
A long petiolar tube furnished with absorbent hairs is formed, and the 
plumule eventually escapes owing to the splitting apart of the component 
members of the tube at its base. The tuber in this species appears to 
be partly epicotyledonary in origin at the commencement, though no doubt 
later the hypocotyl shares in its development. Owing to lack of material, 
the tuber development could not be followed. 
