172 Dr. Hookahs Flora Antarctica. 



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mule, separated by much gelatine ; and 3d, an elliptical core placed 



in the long axis of the petiole, composed of still smaller cells, sep- 

 arated by broader masses of gelatine, which latter is permeated 

 by canals, full, as are the small cells, of chromule." 



" 2. Each ramulus, from which proceed the two petioles, whose 

 structure we have just described, presents no very important dif- 

 ference from them : the core no longer stretches across it, how- 

 ever, but the whole petiole within the superficial portion is aug- 

 mented by a newly developed though indistinct zone of cellular 

 tissue, thus deposited between the superficial (or cortical) and in- 

 termediate 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 longer 

 and the spaces between them narrower ; little or no change is per- 

 ceptible 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 (ail 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 pe- 

 riods of growth. 



14 From this time forward the normal mode of growth followed 



] 



by the stem, exhibits an additional layer or zone of cellular tissue 

 for every subdivision 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. 



" I have stated the growth of the Lessonia to be very rapid ; 

 this is proved by the zones of a five-ridged stem being progress- 

 ively 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 favor the opinion that these Algae attain their 

 enormous bulk in a very few months. 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. 



11 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 contain an axis of tissue different 

 from that forming the greater part of the trunk : here, however, 



