42 



Dansk Botanisk Arkiv, Bd. 2. \"r. 6. 



Fig. 2tx Halophila spinu- 

 losa. A pair of leaves 

 one of which encloses 

 a male llower bud. ( s / 3 

 nat. size). 



The shoots of H. spitiulosa 

 (see Fig. 25) have a superficial 

 (ecological) resemblance to the 

 assimilative shoots of some 

 species of Caulerpa (e. g. C. 

 crass i folia). 



The leaves are broad- 

 linear, 13 — 16 mm long and 

 3 — 4 mm broad, with a spinu- 

 lose-serrate margin, and three 

 parallel veins, besides some very tine anastomosing 

 veins. At the base of the downward-turned side, 

 each leaf has an ear-shaped upwardly bent dilata- 

 tion with an entire margin (Fig. 26). In this pocket 

 the lower part of the llower, when present, is hid- 

 den. The insertion of the two leaves of each pair is 

 exactly opposite: the "ear" is found on the same 

 side of all the pairs ; thus on the right half of a shoot 

 all the leaves have the ears turned towards the ob- 

 server, while he sees the back of all the leaves of 

 the left half. There is, consequently, no alternation 

 as is the case with ordinary opposite leaves. 



The structure of the lea- 

 ves l does not show any 

 important difference from 

 those of other species of 

 the genus. The leaves 

 consist of the two epi- 

 dermal layers only, except 

 round about the veins (Fig. 

 28). The outer walls are 

 not undulating (faintly 

 undulating on the outer 

 side of the ear-shaped dila- 

 tation). Around the middle 

 vein some small air chan- 

 nels are present. The spi- 

 nulose margin is made up 



Fig. 27. Halophila spinulosa. Trans- 

 verse sections of a leaf: a, at the 

 middle: b. near the base. Air cham- 

 bers are shown as circles, veins as 

 black dots. (About 20 x nat. size). 



1 Compare C. Sau vag eau, 1. c. (1890) 294. 



Fig. 28. Halophila spinulosa. 

 Transverse section of a leaf. 

 The veins are shown as black 

 dots, x denotes air chambers. 

 (About M /, nat. size). 



