SECT. ii. CYSTOSEIRA. 255 



pear shape, and sends out from its narrow end filaments 

 or footstalks containing solid yellow grains at their ex- 

 tremities, where a hook or claw is formed by which it 

 fixes itself to rocks or stones. The spore then divides itself 

 into four equal cells of a brown colour, and by the con- 

 tinued subdivision of these into four, the plant increases 

 in size, and assumes a form corresponding to the genus 

 and species of the spore. Dr. Carpenter mentions that in 

 the Fucacese there is also a multiplication by zoospores. 

 These bodies are produced within certain of the cells 

 that form the superficial layer of the frond, and swim 

 about freely for a time in the water after their emission, 

 until they fix themselves and begin to grow ; but these 

 are merely gemmae. 



All the Fucacese are tough leathery plants. This is 

 even characteristic of the genus Cystoseira, various 

 species of which may be seen on our coasts at low water 

 mark, or in the tide pools. They are little shrub-like and 

 somewhat thorny plants, not more than three feet high, 

 with a cylindrical stem and many branches, near the 

 extremities of which there are inflated air-vessels, some- 

 times two or three together ; in some species they are 

 lower down. Long spiny conceptacles are situated at 

 the tips of the branches, but the endochrome does not 

 divide in the germ cells as it does in the Fuci, so that 

 each cell produces but one spore. 



' Throughout all latitudes the two divisions of Fuca- 

 ceae Fucoidese and Cystoseirese, form the prevailing 

 marine vegetation to which the name of sea- weed is com- 

 monly applied, and the different genera so arrange them- 

 selves as to present, with a few exceptions, a most harmo- 

 nious assemblage.' e None of these approach the tropics ; 

 the Fucoidese abound towards the poles, and there attain 

 their greatest bulk, diminishing rapidly towards the 

 equator, and ceasing some degrees from the line itself; 

 while the immense genus Sargassum finds its maximum 



