8 FUNGUS-FLORA. 



this sense a knowledge of the habitat is one factor of value 

 in discriminating between morphologically closely allied 

 species. 



Examination. A few hinis on the use of different re- 

 agents for emphasizing doubtful points have already been 

 given ; and remembering the numerous imperfect statements 

 to be found in many books, respecting matters of microscopic 

 detail, as the form and septation of paraphyses, septation of 

 spores, and nature of ornamentation of the epi spore, it may 

 be repeated that the substitution of very dilute potassic 

 hydrate for water will frequently reveal, clearly defined, 

 septa that could not be seen, or at most vaguely, when 

 examined in water. In the case of working with material 

 that has been dried, the use of potassic hydrate is a neces- 

 sity, the parts of the section, as hairs, paraphyses, spores, &c, 

 expanding much better than when water alone is used, 

 esioecially if the slide is heated over a spirit-lamp until the 

 liquid just boils, the cover-glass being kept in position by a 

 spring-clip. On the other hand it is equally important not 

 to abuse the use of potassic hydrate by using too strong a 

 solution, or by prolonged boiling in this medium, otherwise 

 the cell-walls become swollen, and an appearance is produced 

 quite foreign to the specimen under normal conditions. It 

 is possible to treat coarsely warted spores with potassic 

 hydrate until the wall becomes so much swollen as to appear 

 quite smooth, or in fact until it disaj^pears altogether. When 

 a section is very delicate and too transparent to show the 

 details, a drop of dilute solution of iodine will make it stand 

 out sharp and clear. 



When it is desired to make a thorough study of the mor- 

 phology of a species, it should first be placed in alcohol, and 

 allowed to remain for some days at least. By adopting this 

 method the specimen is rendered firm, and the whole struc- 

 ture at the same time made quite clear. When collecting, it 

 is always advisable to carry a bottle containing methylated 

 spirit, into which specimens intended for critical examina- 

 tion can be placed. These can afterwards be placed in 

 absolute alcohol, or will work quite well if only kept in 

 methylated spirit, and in this medium they can be kept for 

 any length of time — the longer the better — before being 



