2 INTRODUCTION. 



A certain amount of experience and knowledge of the subject greatly facilitates 

 the collection of these plants, but scarcely so much as in other departments of cryp- 

 togamic botany, since most of the species are so small that the most experienced 

 algologist does not know how great the reward of the day's toil may be until he 

 places its results under the object glass of his compound microscope. In order to aid 

 those desirous of collecting and studying these plants, I do not think I can do 

 better than give the following hints as to when and where to find, and how to 

 preserve them. 



There are three or four distinct classes of localities, in each of which a different 

 set of forms may be looked for. These are : stagnant ditches and pools ; springs, 

 rivulets, large rivers, and other bodies of pure water ; dripping rocks in ravines, 

 &c. ; trunks of old trees, boards, branches and twigs of living trees, and other 

 localities. 



In regard to the first — stagnant waters — in these the most conspicuous forms 

 are oscillatorise and zygnemacese. The oscillatoriae may almost always be recog- 

 nized at once, by their forming dense, sliipy strata, floating or attached, gene- 

 rally with very fine rays extending from the mass like a long, delicate fringe. 

 The stratum is rarely of a bright green color, but is mostly dark ; dull greenish, 

 blackish, purplish, blue, &c. The oscillatoriae are equally valuable as specimens 

 at all times and seasons, as their fruit is not known, and the characters defining 

 the species do not depend upon the sexual organs. The zygnemas are the bright 

 green, evidently filamentous, slimy masses, which float on ditches, or lie in them, 

 entangled amongst the water plants, sticks, twigs, &c. They are only of scientific 

 value when in fruit, as it is only at such times that they can be determined. 

 Excepting in the case of one or two very large forms, it is impossible to tell with 

 the naked eye with certainty whether a zygnema is in fruit or not; but there are 

 one or two practical points, the remembrancfe of which will very greatly enhance 

 the probable yield of an afternoon's search. In the first place, the fruiting season 

 is in the spring and early summer, the latter part of March, May, and June being 

 the months when the collector will be best repaid for looking for this family. 

 Again, when these plants are fruiting they lose their bright green color and become 

 dingy, often yellowish and very dirty looking — just such specimens as the tyro 

 would pass by. The fine, bright, green, handsome masses of these algae are rarely 

 worth carrying home. After all, however, much must be left to chance; the best 

 way is to gather small quantities from numerous localities, keeping them separate 

 until they can be examined. 



Adhering to the various larger plants, to floating matters, twigs, stones, &c., in 

 ditches, will often be found filamentous algae, which make fine filmy fringes around 

 the stems, or on the edges of the leaves; or perchance one may meet with rivulariae 

 or nostocs, &c., forming little green or brownish balls, or indefinite protuberances 

 attached to small stems and leaves. These latter forms are to be looked for 

 especially late in the season, and whenever seen should be secured. 



In the latter part of summer, there is often a brownish, gelatinous scum to be 

 seen floating on ditches. Portions of this should be preserved, as it frequently con- 

 tains interesting nostocs and other plants. 



