The Morphology of Ruppia Maritima. 97 
tures in Althenia fiiformis, which he erroneously believed to be 
stipules. 
b, Function. 
The nature of these “ sguamulae intravaginales” points to their ser- 
ving the purpose of secreting organs. Schenck (1886, p. 9) is of 
the opinion that their secretion, which covers the growing point, 
is a protection against parasites, but of this point he is not certain. 
F, Miiller (1877) had already claimed that the slimy secretions of 
such cells protected the delicate growing points from immediate 
contact with the surrounding water, a position which Schenck 
(1886, p. 10) criticizes by asserting that it is difficult to see how 
the outside water could injure the growing points. But Schilling 
(14894), who has made a special study of the subject, returns to 
Miiller’s view. He shows that the slime is impermeable to certain 
salts, &c. in solution in the water, and is probably only developed 
until the epidermal tissue and cuticle are far enough advanced to 
make such protection unnecessary. 
Schilling’s arguments are reasonable. The growing point is an 
extremely delicate part and might easily be injured by the salts or 
other substances in solution in the surrounding water. Especially 
is this true of Ruppia, a plant of salt or brackish waters. This would 
be an omnipresent danger to the young growing parts: the attacks 
from parasites would be intermittent or rare. 
D. Subfloral Leaves 
Although along the stem the leaves are distributed at fairly 
regular intervals, just below a flower they approach each other so 
closely as to appear opposite (PI. VU, fig. 35; Text-fig. 18), a char- 
acteristic common to many other members of the family, notably 
Zannichellia, Althenia, Potamogeton, &c. 
These two apparently opposite leaves, which I have designated 
the subfloral leaves, besides differing from the ordinary foliage 
leaves in their mode of arrangement, possess slightly specialized 
sheaths and considerably shorter leaf blades. The sheath of the 
outer or lower leaf envelopes that of the inner, while the sheath 
of the inner or upper leaf surrounds the peduncle, and both together 
form a protective envelope for the young flower before it elongates 
(Pl. Il, fig. 6; Pl. VI, fig. 35). As a result of these conditions, the 
sheaths are slightly wider than those of the ordinary leaves, and 
they as well as the leaf blades are also shorter, the latter character- 
istic being in harmony with the bracteal nature of these leaves. 
