308 Transactions. — Botany. 



near the base of the plant and not immediately below a fork, 

 (PI. XXXIX., fig. 2, a.) 



The growth in length, as in other Laminarians, takes place 

 at the junction of the stipe and the frond, and consequently, 

 the tip of the frond being once worn off by the action of the 

 waves, or eaten by molluscs, it cannot be replaced, and, as all 

 fronds subsequently formed have no apices, a complete leaf is 

 rarely to be found except in young specimens, in which, as has 

 already been stated, they are much longer than in the mature 

 forms. Harvey (loc. cit.) explains the absence of the tip in L. 

 fuscescens thus : "In the present species the sori are situated 

 beyond the middle of the leaf ; they are oblong and nearly as 

 broad as the lamina, of which they carry away the upper part 

 when decaying, causing the apices to be two-horned. In none 

 of the specimens is the point perfect, all the spores we have 

 seen being situated on the sorus, which has itself fallen away 

 from the edge of the frond." I have not noticed that the 

 sorus in L. varicgata falls away in the manner described. It 

 is certainly frequently attacked by a green filamentous alga 

 which grows on its upper surface, on the tops of the paraphyses, 

 and causes decay ; but this green alga, though chiefly found 

 forming a velvety nap on the sorus, grows elsewhere on the 

 surface of the frond. 



Notes on the Histology. 



The Frond. — A transverse section through the frond shows 

 it to consist of an epidermal and several cortical layers gradu- 

 ally merging into a parenchymatous tissue. In the centre is 

 the hyphal layer, in which, however, the hyphae preserve a 

 general longitudinal direction. Like the stem, it contains 

 "trumpet hyphae." Immediately under the epidermis are a 

 number of large lacunae (Plate XL., fig. 3, a). It is on these 

 that Agardh ap^Darently chiefly relies to distinguish this 

 species from others. Under a Browning's platyscopic lens I 

 have counted as many as twenty-five of these in a transverse 

 section of a single frond. They open into ostioles on the 

 surface. The structure of the frond is the same on both sides. 

 I have not seen any "air-cells," as figured by Hooker and 

 Harvey in the centre of the frond. — ("Flora Antarctica," 

 vol. h., pi. 167c.) 



The Stem. — Harvey, in speaking of L. fuscescens, says 

 ("Flora Ant.," vol. ii., p. 458), "The trunks, which contract to 

 a quarter of their original dimensions when dry, and become 

 deeply furrowed, are perfectly smooth and cartilaginous when 

 fresh. On being cut across, the curious appearance of con- 

 centric elliptical rings, in many respects very similar to, 

 though very different from, those of an exogenous trunk, is 

 very evident." Harvey again refers to this appearance in 



