INTRODUCTION TO CRYPTOGAMIC BOTANY. 187 



or both. Nemalion virens occurs on the Pacific coast of 

 Mexico ; Nemalion multijidum is not uncommon on our rocky 

 coasts, occupying frequently the shells of Balani. Besides 

 the central threads and horizontal filaments, others are given 

 off from the latter after the fashion of roots, a circumstance 

 which occurs in other Algse, as for instance in Leathesia 

 Berkeleii, and some Chcetopliorce. Agardh compares the 

 development of the frond to that of an endogenous stem. It 

 consists of a medullary stratum formed of longitudinal simple 

 filaments, an intermediate layer of obliquely horizontal anas- 

 tomosing filaments, and a periphery of horizontal dichotomous 

 fastigiate filaments. The descending threads are doubtless 

 analogous to those of Callithamnion ; and if the branches were 

 increased infinitely in number, and still sent down their 

 descending filaments, we should have very much the same 

 structure. Helriiiinthora divarlcata is also an inhabitant of 

 similar coasts, extending with the last to the northern parts 

 of our island. Both were found at Appin, by Captain Carmi- 

 chael, and pointed out to me there by him in 1824*. Liagora 

 differs from the rest in appropriating a large quantity of cal- 

 careous matter in which it resembles the strictly analogous 

 flat-fronded or cylindrical Chcetophorce, though other species 

 of that genus abound in crystals of carbonate of lime. 

 Liagora, when dry, often asssumes a green tinge, which makes 

 the resemblance the closer ; but when fresh it has the colouring 

 proper to the Rhodosperms. 

 7. Squamari^, J. Ag. 



Frond lichenoid, crust-like, rooting beneath. Spores in 

 moniliform strings, lodged in wart-Hke excrescences. 



164. Besides those florid, chain-spored Algse, which have con- 

 ceptacles, either entirely distinct from the frond, slightly im- 

 mersed at the base, or absolutely naked, there are others whose 

 fructifying nucleus is not lodged in a hollow concej^tacle, but 

 in wart-like excrescences in the frond itself This is a small 

 division, and consists of Alga3, with licheniform fronds, pro- 

 ducing warts on their upper surface, which contain tufts of 

 moniliform threads. The only certain tenants of this division 

 are Peyssonnelia, which was proposed originally by Decaisne, 



