4fi0 FLORA ANTARCTICA. [Fuegia, the 



different textures, all, however, very gelatinous, and modifications of the three layers forming the leaf, there are 

 1st, the superficial tissue (or cortex) consisting of small cells, closely packed and full of chromule, gradually opening 

 out into, 2nd, an intermediate tissue of much larger cells more loosely placed, with little or no contained chromule, 

 separated by much gelatine ; and 3rd, an elliptical core placed in the long axis of the petiole, composed of still smaller 

 cells, separated by broader masses of gelatine, which latter is permeated by canals, full, as are the small cells, of 

 chromide. 



2. Each ramulus, from which proceed the two petioles, whose structure we have just described, presents no very 

 important difference from them ; the core no longer stretches across it, however, but the whole petiole within the 

 superficial portion is augmented by a newly developed though indistinct zone of cellular tissue, thus deposited between 

 the superficial (or cortical) and intermediate tissue. At this period the cortex is somewhat broader, and the 

 intermediate tissue has become, through the absorption of the gelatine, much more conspicuous ; the cells being 

 larger and the spaces between them narrower ; little or no change is perceptible in the core itself. 



3. The branch is very materially different from either of the above, for what was hitherto the petiole is now 

 enclosed (all but its cortex) in a very broad zone of cellular tissue, whose cells are large and thin towards the 

 old tissue, elongated and of a different shape, so as to show the line of separation between the two periods 

 of growth (see B 1, of the plate Lessonia). 



From this time forward the normal mode of growth followed by the stem exhibits an additional layer or 

 zone of cellular tissue for every subdivison of the frond, (shown at A 1, where six are interposed between 

 the cortex and core). It is not probable, however, that this numerical relation can be always evident, or that 

 the number of subdivisions of the frond will indicate the rings of growth in a large stem. This uncertainty 

 arises from the branches being frequently broken off ; added to which, the growth of the sea-weed is very rapid, 

 and there being no period of rest, irregular zones may be expected, or their absence from those branches of the plant 

 whose leaves are injured. 



In their anatomy the stems of L.fuscescens and L. nigrescent do not differ much from that of this species, 

 except that the air-cells are copious in the stems of the former, and much rarer in the latter ; in which also 

 the cortical substance is much broader. 



In the elegant Lessonia Sinclairi, Harv. MSS., from California, the stipes (which bears but a solitary linear 

 frond) is terete, and in the specimen we examined, contains a central core, reaching half-way across the diameter. 

 There are apparently two rings of tissue beneath the cortex, separated by a zone of very large cells (air-cells ?) ; 

 whence it is difficult to account for the stem being terete, for the frond is plane, and the core three times longer 

 than broad. Nor is it easy to explain the origin of the two zones surrounding the core ; if they really be succes- 

 sively deposited, it is possible that the frond is two years old ; if not, that the large cells are air-cells, and do not 

 indicate a line of separation between two successive deposits. 



I have stated the growth of the Lessonia to be very rapid ; this is proved by the zones of a five-ringed stem 

 being progressively broader towards the circumference. The probability, too, of one being added for every time the 

 laminae divide, and the fact that the process of subdivision is continued in geometrical progression, all favour the 

 opinion that these Algce attain their enormous bulk in a very few mouths. The vast masses washed up on the outer 

 eastern shores of the East Falkland Island, and the rapidity with which they decay, are additional proofs of a singularly 

 rapid development. 



The analogy between the mode of growth exhibited by this genus and an Exogenous tree, is, though incomplete, 

 very obvious ; both increase by layers deposited outside one another, within a cortical substance, and both con- 

 tain an axis of tissue different from that forming the greater part of the trunk : here, however, there are no 

 traces of medullary rays. We conclude this subject with the observation, that the periodical increment of the 

 trunk being dependent on, or coincident with, the formation of the laminae, these appear to perform the office of the 

 leaves in the higher order of plants ; and that the Lessonia is also in this respect analogous to an Exogenous plant, 



