VI INTRODUCTION. 



in greenhouses and hothouses, warm springs, outlets of warm 

 water from steam engines, brackish ditches, all these have their 

 own peculiar forms, and experience will soon prove that where 

 the favourable condition of quiet humidity is found, search will 

 seldom be in vain. Of course, during exceptionally dry 

 weather localities which would otherwise give satisfaction may 

 produce nothing but disappointment. 



The methods of collecting do not much differ from those 

 adopted for other kinds of pond life. A japanned case with 

 from six to twelve corked test tubes will usually suffice for a 

 day's collecting. Filamentous Alga?, such as S'pirogyra, Clado- 

 phora, &c., may be wrapped singly in paper, and a number of 

 these packets can be contained in a small tin box. It is always 

 essential to keep each " gathering " by itself. 



Preservation for future study, or for the herbarium, will be 

 secured by the usual methods of floating and mounting marine 

 Alga?, first cleansing the specimens by well washing in a flat 

 dish or soup-plate, and finally passing under them a slip of 

 clean white paper, which is raised so as to take up the Alga? in 

 the middle, well floated into position, draining off the water, 

 and then drying, with the least pressure possible. For minute 

 species, and small specimens, thin flakes of mica are preferable 

 to paper, for many reasons, especially that they can be placed at 

 any time under the microscope and examined. The Palmel- 

 lacece, and similar groups, will be of very little service if dried 

 in any other way. Most species will adhere of themselves to 

 either paper or mica, the exceptions, such as Vaucheria and some 

 Cladophorce, can be fixed with gum tragacanth. 



Some difficulty may probably be experienced in mounting 

 satisfactorily specimens for the microscope. We have seen 

 " slides " in which the specimens were still green and life-like 

 after having been mounted for twelve years in the water in 

 which they were collected, but unfortunately there is always a 

 risk of leakage with mounts in fluid, If the medium is denser 

 than the contents of the Alga? cells, the endochrome will be 

 contracted and the walls collapse. One objection to mounting 

 in glycerine, or glycerine and water, is the density of the 

 medium, and consequent collapse of the cells ; another, that in 



