SEA WEEDS 373 



and are often anything but beautiful when dried and mounted, yet 

 in their fresh condition they are generally pretty objects, and their 

 microscopic structure is particularly interesting on account of 

 the beautiful and symmetrical arrangement of their siphons and 

 tubes. 



If the reader is the fortunate possessor of a compound micro- 

 scope, it will amply repay him to make transverse sections of the 

 fronds for examination. A short length of the frond should be 

 inserted into a slit cut in a piece of carrot or elder pith ; and, while 

 thus supported, very thin transverse sections may be easily cut with 

 a sharp razor, care being taken to keep both razor and object very 

 wet during the process. Allow the sections to fall into a vessel of 

 water as they are cut, and then select the thinnest for examination, 

 mounting them in a drop of water in the usual way. 



Specimens in fruit should always be obtained when possible, so 

 that the nature of the fructification may be observed. Two kinds 

 of spores may be seen in each species, but, as is usually the case 

 with the red sea weeds, on different plants. Some are small pear- 

 shaped bodies, enclosed in oval cells at the tips of the fronds ; and 

 the others are arranged in clusters of four in swollen parts of the 

 threads. 



The commonest species is P. fastigiata, which may be found 

 in abundance as bushy brownish tufts on the fronds of Fucus 

 nodosus (p. 386). A transverse section 

 of this weed is a very beautiful micro- 

 scopic object. It resembles a wheel, with 

 a dark centre to the nave, and several 

 spokes enclosing about sixteen regularly 

 arranged tubes. The swollen tips of fronds 

 should also be examined for the urn- 

 shaped cells containing the spores ; and 

 if a gentle pressure be applied to the 

 cover-glass with a needle, the little pear- 

 shaped spores may be expelled. The other Flo 2 56. Polysiphonia 

 kind of spores may be found near the fastigiata 



bases of the branches on different plants. 



Among other species we may briefly mention P. parasitica, 

 sometimes found near low-water mark, growing in little feathery 

 tufts of a bright-red colour, on the lichen-like Melobesia or on 

 corallines. It has seven or eight parallel siphons in its fronds, all 

 regularly arranged round a small central space. 



