THE GREEN ALGAE OF NORTH AMERICA 87 



beautifully some particular structure, but here too, permanence 

 is far from assured. Moreover the slide shows just the one 

 thing in the one position ; there is no changing or moving it. 



There are some genera of tropical algae that can be prepared 

 for the herbarium practically the same as flowering plants (cal- 

 careous algae like Halimcda, and coarse non-calcareous forms 

 like Avrain-cillca) by pressing between driers and then strapping 

 or gluing to herbarium sheets. Of green algae of temperate 

 regions Ulva and some species of Cladophora and Chactomorpha 

 are all that can be treated in this way ; most species that are 

 of sufficient size for the individual fronds to be shown (Bryopsis, 

 most Cladophoras) should be mounted on paper, and the paper 

 attached to the herbarium sheet ; the plant should be allowed 

 to spread out in natural form in a shallow dish or pan of 

 salt water, the paper placed under it and carefully raised, 

 until it, with the undisturbed specimen, is lifted out. The 

 papers are then placed on driers, specimens up, a piece of 

 cotton cloth the size of a drier laid over all ; then another drier, 

 specimens, cloth, etc. After this the process is much as for 

 flowering plants ; greater or less pressure according to the char- 

 acter of the specimens ; changes of driers as fast as they become 

 moist, but no change of cloths ; these not to be removed until 

 specimens are thoroughly dry and ready for the herbarium. 

 The heaviest driers should be used, as the amount of moisture 

 to be taken up is so much more than in land plants. Frequent 

 change of driers, and having them thoroughly dr}^ when used, 

 will add much to the value of the specimens. Nearly all algae 

 prepared in this \vay will adhere to the paper. 



Those forms in which the individual plants are minute 

 (Codiolum, Prasinodadus) of course cannot be treated in this way ; 

 a small portion of the thin pasty mass can be spread with a 

 knife on a piece of paper, and then dried without cover or 

 pressure. It is sometimes better to use mica instead of paper 

 for very minute forms; they are then ready, when moistened, 

 for microscopic examination, without removing from paper to 

 slide. Where mica is used and a large number of specimens 

 are to be prepared, it is often convenient to add more water and 

 drop from a pipette on the mica. 



