monest of the genus Elachistea. It infests Fucus vesiculosus and 

 F. serratus almost wherever these plants grow, and may be 

 found nearly at every season. At its first appearance it forms a 

 minute pencil of greenish filaments rising from a scarcely per- 

 ceptible tubercle. As it grows larger, the colour changes to 

 brown, and the tubercle increases much in size, and at length 

 becomes a button, attached by a central point. It then falls 

 away and the plant perishes. The growth of other Elacldstece 

 is very similar. 



By J. Agardh this genus is placed in Ectocarpece, but, in my 

 opinion, incorrectly. The structure of the tubercle, in which the 

 spores are lodged, is precisely that of the Chordariece, and did 

 this tubercle constitute the whole plant, no doubt Professor 

 Agardh would associate the genus with the latter family, for the 

 whole structure of this part is analogous to that of Zeat/iesia, and 

 the nature and position of the spores the same. But then there 

 are the long pencilled filaments composing the largest part of the 

 frond; and these are very unlike anything found elsewhere in 

 Chordariece, while they closely resemble the threads of an Ecto- 

 carpus in structure. Taking these filaments for the frond, Agardh 

 would be correct in referring the genus to Ectocarpece. But, to 

 my mind, the tubercle, as it contains the fructification, must be 

 regarded as the most essential part of the structure ; Wis filaments 

 as an accessory part ; and therefore I am of opinion that the 

 genus is best placed in Cliordariece. 



Fig. 1. Tufts of Elachistea fucicola, growing on Fucus vesiculosus; — the 

 natural size. 2. Part of a branching filament of the tubercle, with its para- 

 nemata, and excurrent filaments, one of which is bent back, the others cut 

 off. 3. Portions of one of the excurrent filaments. 4. Paranemata and spore. 

 5. Spores in various stages of advancement; — all magnified. 



