318 Transactions. — Botany. 



Art. XXXIX. — On the Structure of Hormosira billardieri. 



By T. A. MoLLET, 



[Read before the Philosophical Institute of Canterbury, ith November, 1880.] 



Plates XIII. and XIV. 



The genus Hormosira, which belongs to one of the three sub-orders of the 

 Algae, the Fucacere, is described by Hooker in his " Handbook of the N.Z. 

 Flora" as follows: — "Root discoid. Frond olive-brown, without distinct 

 organs, dichotomously branched, moniliform, internodes inflated, fertile. 

 Fruit dioecious. Conceptacles sunk in the periphery of the internodes, con- 

 taining subsessile n arrow- pyr if orm spores and unbranched paranemata." 



This genus, confined to Australian and New Zealand seas, has as its 

 sole representative the species billardieri: — "Frond 6-18 inches long, very 

 variable in size and robustness ; internodes obconical, wingless." After 

 thus describing it. Hooker mentions three varieties — hanksii, lahillardieri, 

 and sieheri ; but many of the features of these occur in the seaweed forming 

 the subject of this paper. In fact, the shape of the internodes is far from 

 being constant, and it must be admitted, as has been done by Harvey,* that 

 the various forms described are most probably one and the same. 



In " Phycologica Australica "t the different forms will be found figured, 

 and, after describing them, the author concludes by supposing them all to 

 be one species, varying slightly, due to the different conditions of growth, 

 such as exposure, depth of water, etc. 



The branching of this seaweed is generally dichotomous (commonly so- 

 called), but is very often trichotomous, either irregular on the summit of the 

 internode, or the three branches placed at equal intervals along the upper 

 edge (PL XIV., fig. 1). It is not unusual to see as many as four branches 

 springing from one internode (PI. XIV., fig. 2), and in two or three cases I 

 have noted six. 



At times lateral branches are found (PI. XIV., figs. 2 and 3). Inter- 

 nodes are also occasionally found united towards their base (PI. XIV., 

 figs. 4 and 5). This junction might at first sight appear to be a node, with 

 two internodes springing from it ; but the fact of its being hollow and in 

 communication with their two cavities precludes the possibility of such an 

 idea. 



A most important point not mentioned in any of the works I have had 

 access to (including the Australasian Floras in the Christchurch Public 

 Library), is that the branching does not always take place from the inter- 



* In the section Algse, Hooker's "Flora of Tasmania," Vol. II., p. 285. 

 t "Phycologica Australica," Harvey, Vol. , pi. 135, 



