Hill. — Studies in Seed Germination. 
221 
When the petioles have become split into their several strands, it is 
found that the vascular bundle of each is surrounded by a band of peri- 
cyclic tissue of recent formation, and in an active state of division (Text- 
fig. 2). This pericyclic periderm gives rise to suberized tissue on the outer 
side and cortical tissue on its inner side, and the line of communication 
between the seed and the young plant is thus maintained for a considerable 
time during the seedling’s development. 
The vascular bundle contains a small number of lignified elements, 
but consists mainly of small sieve-tubes and phloem parenchyma. 
Summary. 
1. On the germination of the seed in Mar ah, the petioles, which are 
fused together to form a tube, grow out and carry the plumule and radicle 
into the ground. 
2. In M. fabaceus the tube is very short and the germination is almost 
normal, but in M. horridus and other species the petiole tube elongates 
considerably and is furnished with absorbent hairs. 
3. The radicle breaks through at the base, and later the plumule 
penetrates the side of the petiole tube and grows above the soil. Even- 
tually a hypocotyledonary tuber is formed, which may become very large. 
4. In M . horridus the petiole tube first splits into its two component 
halves and then, owing to the growth of the tuber, into six separate 
strands, each of which is furnished with a vascular bundle. 
EXPLANATION OF PLATE V. 
Figs. 1 and 2, Marah fabaceus. Figs. 3-7 and 9, M. horridus. Fig. 8, M. macrocarpus. 
Fig. 1. Marah fabaceus. Early stage in the germination of the seed, showing the short petiole 
tube (/.), with its tissues frayed and the radicle bent downwards. The plumule has not yet broken 
through the petiole tube. t. testa ; c. cotyledons. 
Fig. 2. An older seedling. The plumule (j 1 .) has broken through the tube at the point of curva- 
ture of the tube and radicle. 
Fig. 3. M. horridus. A seed with a portion of the testa removed, showing the petiole tube 
with a cap ( 'x .) at its apex. The tube measured 1*5 cm. in length and was furnished with a mass 
of absorbent hairs. (Slightly mag.) 
Fig. 4. The flange-like cap ( x .) at the apex of the petiole tube. (Mag.) 
Fig. 5. The apex of the petiole tube in diagrammatic section, showing the undeveloped plumule 
(j.), radicle ( V .), and the epidermal hairs. 
Fig. 6. The apex of the tube, showing the cap. (Mag.) 
Fig. 7. An older seedling in which the petiole tube has elongated and the root developed. 
The point of junction of petiole tube and root is marked by a slight swelling. The testa has been 
removed. The whole length of tube and root is 7-5 cm., the tube measuring 3*5 cm. (Nat. size.) 
