y. CERAMIACE.E. 219 



cortical stratum of cells ; the inner cells of the cortical layer roundish, the outer 

 minute, coloured. Favelloe terminal on the lesser ramuli, involucratcd with numer- 

 ous ramelli, containing within a hyaline periderm, numerous angular spores. Tetra- 

 spores on the ultimate pinnules, external, sessile, solitary or aggregate, formed each 

 from an internode of the ramulus, roundish, triangularly divided. 



A beautiful genus, strongly marked by its decompound-pinnate, distichous, in- 

 articulate, or, rather, internally articulate fronds, which ai*e of larger size, firmer 

 texture and more opaque than in most other genera of this Order. All are 

 branched on a pinnate model. In some the pinnce and pinnulae are regularly alter- 

 nate throughout the branches and lesser divisions. In others they are as regularly 

 opposite ; but among those with opposite pinnaj two varieties of ramification must 

 be carefully distinguished. In some the opposite pinnee are of the same nature, 

 either of equal length and exactly similar, or one longer than the other, a longer 

 and sliorter pinna alternating regularly at each side of the rachis. In others, the 

 opposing pinnae are of different natures ; one of them phyllodium-like, always 

 remaining unchanged after having once been formed, either entire, serrate or pecti- 

 nate ; the other branch-like, pinnately-compound, at first shorter and simpler, 

 afterwards lengthened and decompound in similar manner to the larger branches of 

 which it is a pinna. The pinnaj opposite the phyllodia are often abortive or little 

 developed ; whence arises an irregularity of ramification in most species. Often 

 too they are very much reduced in size and converted into racemes of fructification. 



Sect. 1. Diversifoli^ : Pi7ince opposite, of different nature, one leaf -like undivided^ the 

 other (sometimes obsolete) branch-like, pinnatedly-comjMund. 



1. Ptilota densa, Ag.; frond piano-compressed, two-edged, decompound pinnate; 

 pinnte opposite, unlike ; one undivided, falcate, inciso-pectinate along its outer edge ; 

 the other compound, either lengthening out into a branch, or minute and ramuli- 

 form ; branches linear, densely set with the falcate pectinifid pinna} and opposing 

 minute multifid ramuli ; tetraspores in oblong glomerules alternating with the pm- 

 nulEB of the multifid ramuli. /. Ag. Sp. Alg. 2, p. 98. Ptilota pectinata, Harv. in 

 Beech. Voy. p. 164. (Tab. XXXII. B.) 



Hab. California, Lay and Collie, (v. s. in Herb. T. C. D.) 



Frond several inches long, half a line in diameter, more or less compressed, 

 decompound-pinnate, but very irregular in the development of its major pmme, 

 though perfectly regular in the system of construction. Sometimes the major 

 pinniB are closely set and furnished with a second or third series also closely placed 

 together ; sometimes (as in the specimen we have figured) they arc widely distant 

 and very unequal in length. Both the larger and lesser branches are opposed, at 



F F 2 



