INTBODUCTION TO CEYPTOGAMIC BOTANY. 211 



conditions of sptasrical-spored species. In E. pusillus, both 

 spores and silicules are produced upon the same thread. 



195. As regards geographical distribution, they are abun- 

 dantly scattered throughout the temperate regions of the 

 northern hemisphere, both on the British and American coasts, 

 but they occur also in the Mediterranean ; and some of the 

 northern species appear again in the southern hemisphere, as 

 at Cape Horn and New Zealand. 



196. Ectocarpus, which abounds in species, is remarkable 

 for the variety of forms under which the zoosporic fruit ap- 

 pears, affording a number of beautiful microscopic objects, and 

 strictly definiag species which would otherwise be unintelligible. 

 In most species of Ectocarpus the threads are distinct, but 

 from their flaccid nature they easily become entangled, and 

 in consequence one or two species form spongy ropes, which 

 give them a peculiar character. This condition is not, however, 

 essential. While Ectocarpus is distinguished by the flaccid 

 filaments, for the most part irregularly branched, and very 

 seldom putting on any neat or delicate forms, Sphacelaria 

 is, on the contrary, distinguished by rigid threads, often of ex- 

 quisite symmetry, simulating various higher Cryptogams. One 

 of the species peculiar for its abundant racemose fruit has 

 been found only once, a singular instance of the combination 

 of more simple stems than usual, with more highly developed 

 fruit. It is principally a northern genus ; but three or four 

 species occur also in the south. S. scoparia, indeed, appears 

 almost cosmopolitan. To these genera, others succeed with 

 solid stems. Chcetopteris is distinguished by this character 

 alone from Sphacelaria. G. plumosa has its southern limit 

 about the south of England, whUe it extends northward to 

 Greenland and the Arctic Seas. The only remaining species 

 belongs to the southern hemisphere. Cladostephus has the 

 stem and main branches inarticulate, while the ultimate ramuli 

 resemble in structure the lowest form of Melanosperms. The 

 two common British species, easUy known by their densely 

 crowded or verticillate branches, so as to make them resemble 

 little bottle brushes, occur also on the North American coast, 

 and there are one or two species of warmer climates. 



14. * 



