The Morphology of Ruppia Maritima. 97 



tures in Althema filiformis, which he erroneously beheved to be 

 stipules. 



b. Function. 



The nature of these '■'■ squamulae 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 

 (1894), 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 (PL VII, 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 diff"ering 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 pedvmcle, and both together 

 form a protective envelope for the young flower before it elongates 

 (PI. II, fig. 6 ; PI. VII, 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. 



