70 LAURENCIACE^. 



I. LAURENCIA, Lamour. J. Ag. ref. 



Frond solid, cartilaginous, terete or compressed, decompound pinnate, rarely sub- 

 dichotomous, composed of two strata of cells : the medullary stratum of oblong- 

 angular longitudinal cells, longest toward the centre of the stem ; the cortical of 

 roundish angular cells in a subsimple row. Conceptacles ovate, with a terminal 

 pore, containing within a cellular pericarp a dense tuft of pearshaped spores on 

 simple funiculi radiating from a basal placenta. Tetraspores tripartite, lodged 

 without order in a transverse band below the apices of the ultimate ramuli. 

 Antherldia collected in terminal, ^saucer-shaped receptacles. 



Fronds generally fleshy, rarely membranaceo-gelatinous when recent, cartilagi- 

 nous when dry ; often livid purple, rarely a blood or rose-red colour, changing to 

 greenish or yellowish when growing in shalloAv water exposed to sunshine. Sie7n 

 and branches linear, terete or compressed, pinnately compound, the lesser divisions 

 sometimes irregularly forked, or subdichotomous, distichous or branched to all 

 sides ; the branches opposite, alternate or irregularly whorled ; sometimes very 

 irregularly placed. Hamuli slightly constricted at the base, dilated and very obtuse 

 at the summit ; the barren ones simply clavate, the fertile often by the development 

 of rudimentary processes tuberculated or botryoid. Conceptacles formed from 

 the transformation of the ultimate ramuli, mostly ovate. Tetraspores always 

 lodged beneath the ends of the simple or compound ramuli. 



From this genus, restricted by the above character, are now removed all the 

 species (as L. dasyphylla, L. tenuissima and their allies) that have an articulated 

 polysiphonous axis running through the frond. These will be found among BJio- 

 doinelacece under the genus Chondria. The remainder of the Grevillian genus 

 Laurencia constitute a very natural group, dispersed through most parts of the 

 temperate and tropical oceans. Very few occur on the shores of the Northern 

 States, but on the Florida Keys there are many common species, some of them 

 congregating in such masses that a large per centage of the drift seaweed is com- 

 posed of their broken fronds. 



The species are exceedingly difficult of determination. Many intermediate 

 varieties often connect the most opposite looking specimens, and the new species 

 here proposed are not offered without hesitation. Indeed, in this genus, as in 

 many others, it is often impossible to tell whether we are dealing with species or 

 sportive forms without a very careful examination of a number of specimens, or 

 without some knowledge of the circumstances accompanying their development. 



1. Laurencia pinnatifida, Lamour.; frond compressed, cartilaginous, dull purple, 

 bi-tripinnatifid, all the divisions alternate, the ultimate ones obtuse, simple or 

 lobed. Harv. Pliyc. Brit. t. 55. Kiltz. Sp. Alg. p. 856. Harv. in Bot. Beech. Voy. 



