130 SQUAMARIE^. v. 



The frond expands horizontally, and is either closely adnate to the substances on 

 which it lies and to which it is attached by means of minute, root-like processes, 

 forming a thin downiness on the lower surface, or it is attached by its lower half 

 only and free at the extremities. It is either orbicular or variously lobed at the 

 margin, the lobes fastigiate, circumscribed by a curved line and more or less fan- 

 shaped, often lying on one another in an imbricate manner, and marked on the 

 upper surface by faint concentric lines of growth. The substance in the smaller 

 species is delicately membranaceous, in the larger, thicker and more leathery. 

 The structure is entirely composed of cylindrical cellules twice or thrice as long as 

 their diameter and firmly set in filaments which closely cohere together and form 

 the membranous or coriaceous substance. These filaments are disposed in two 

 strata. The lowest are horizontal, radiating from a central point in the orbicular 

 fronds, and from the base of the fan-shaped ones ; they form the substratum or 

 basis of the membrane, and by their development determine its limits. From the 

 upper surface of the membrane so formed spring the obliquely vertical filaments of 

 the upper stratum which are closely combined into a crust of greater or less thick- 

 ness, their length determining the thickness : and as they arise from the radiating 

 filaments of the lower membi'ane, their terminal cells also form radiating lines on 

 the upper surface. 



The fructification is lodged in shapeless, depressed warts irregularly scattered 

 over the upper surface, and formed of vertical confervoid filaments resembling 

 those of the upper stratum but less closely concrete. These warts sometimes con- 

 tain spores, and sometimes tetraspores, on separate plants. The spores are formed 

 consecutively, one in each cell of the vertical filaments, and are therefore set in 

 moniliforra strings, simple or branched according to the nature of the filaments 

 composing the wart. A portion of the wart is thus converted into a sporiferous nu- 

 cleus, the remainder consisting of barren paranemata which serve the purposes of a 

 conceptacle. The tetraspores., in the warts which produce them, are lodged among 

 the bases of the paranemata, several in the same wart, but never placed in strings, 

 each tetraspore being formed of an arrested and transmuted filament. They are 

 pedicellate and at maturity divide into four equal parts placed crosswise. 



The type of this singular genus is the Fucns squamarius of Gmelin ( Tur7i. Hist- 

 t. 244) a native of the Mediterranean, long misunderstood by botanists, and placed 

 by the elder Agardh in Zonaria, to which its flabelliform fronds suggested a rela- 

 tionship. Its true characters were pointed out nearly about the same time by 

 Decaisne and Zanardini, both of whom proposed it as the type of a new genus dis- 

 tinguished alike by external habit and by the curious tetrasporic fructification. 

 Montagne, more recently, has described the sporiferous nucleus and thus completed 

 the generic character. To this original species several have since been added, of 

 which the two following are claimed for the North American flora. 



1. Peyssonnelia Duhyl, Crouan ; frond membranaceous, orbicular or lobed, 

 attached by the whole of its under surface. Crouan, Ann. Sc. Nat. 1844, p. 368, 

 t. 1 1, B. Harv. Phyc. Brit. t. 71. /. Ag. Sp. Alg. 2, p. 501. Kiitz. Sp. Alg. p. 691- 



