252 THE TEACHING BOTANIST 



that Pleurococcus and Spirogyra give the optimum resultant 

 between accessibility and representativeness of their respective 

 groups. Pleurococcus may be found on the damp, shaded 

 bricks and flower-pots of any greenhouses, but, since many 

 other Algae occur in those places, it is necessary to examine 

 the material carefully ; it may be obtained also from the bark 

 of trees, on the damp, shaded side, where, as a green film, it 

 is sufficiently familiar. Protococcus occurs in about the same 

 situations, but, as it reproduces by zoospores only, which are 

 extremely difficult to demonstrate, it is less useful. As to 

 Spirogyra, it is a classic object, and good for many purposes. 

 Conjugating and zygosporic material must be secured the au- 

 tumn before (or may be bought from the Cambridge Botanical 

 Supply Company), and, with vegetative material, may be pre- 

 served in formaline. But much better is material kept all winter 

 in a dish or tank in a greenhouse, as it can then be seen of its 

 natural color and appearance. In all cases the material alive 

 and on its natural substratum should be brought into the labo- 

 ratory. Fucus may be collected on the coast in summer and 

 preserved in formaline, or may be obtained alive and fresh at any 

 time of year from the Cambridge Botanical Supply Company 

 on a few days' notice. For its proper study, sections through 

 the conceptacles are needful, and these may be made by the 

 students themselves with a sharp scalpel, the end of the frond 

 being held between two flat pieces of pith. There is no Red 

 Seaweed known to me which is easily obtainable alive in quantity 

 and in condition to show its reproductive parts to students. I 

 have had to use herbarium specimens of various species for the 

 vegetative structure, and to supply the reproductive structures 

 of a typical form from diagrams, using the Kny series for 

 this purpose. The students copy this diagram with explana- 

 tions ; it is not a good principle, but it is better than nothing. 



