40 PKACTICAL BOTANY. 



with large and obvious "stoppers" on either side of 

 the pit-membrane ; the latter are much thinner, and 

 the presence of the pit-membrane, and " stoppers " is 

 consequently less easy to observe, if indeed they be 

 constantly present at all. 



V. Turning now to the insertion on the frond of 

 Ascophyllum, detach the bases of one or two of the 

 thalli of P. fastigiata from the substratum by means of 

 forceps, noting the firmness of their attachment : mount, 

 and examine under a low power. It will then be seen 

 that towards the base of the thallus single superficial 

 cells are of elongated, cylindrical form, and have thick 

 walls. 



VI. Cut transverse sections of the frond of Asco- 

 phyllum, so as to pass through the insertion of one of 

 the tufts of Polysiphonia : mount as before, and observe 

 under a low power that those elongated, thick-walled 

 cells above described penetrate deeply into the thallus 

 of the host, and thus obtain a firm hold upon it, 

 while their own strongly thickened walls will explain 

 further the strength of attachment. 



For comparison with the above type, observations should also 

 be made on other forms among the Floridese, and the following 

 are suggested as good illustrative examples : 



A. Batrachospermum moniliforme^ Roth., a purplish-brown, 

 slimy-feeling Alga, which grows on stones in fresh- water streams. 

 Observe it fresh, mounted in water, or preserved in weak 

 glycerine, and note under a medium power the central series of 

 cells, which terminates in a dome-shaped apical cell : in the 

 mature parts, the cells of the central series are elongated, as 

 internodes ; while at the nodes are inserted brushes of branched 

 multicellular filaments, often terminating in long fine bristles : 

 in the older parts, some of these filaments are closely applied to 

 the internodal cells, thus forming a sort of cortex. 



