XXXVl INTBODUCTION. 



244. For dissecting and examining flowers in the field, all that is necessary is a pen- 

 knife and a pocket-lens of two or three glasses from 1 to 2 inches focus. At home it 

 is more conTenient to have a mounted lens or simple microscope, with a stage holding 

 a glass plate, upon which the flowers tn&j be laid ; and a pair of dissectors, one of 

 which should be narrow and pointed, or a mere point, like a thick needle, in a handle; 

 the other should have a pointed blade, with a sharp edge, to make clean sections across 

 the ovary. A compound microscope is rarely necessary, except in cryptogamic botany 

 and vegetable anatomy. For the simple microscope, lenses of J, ^, 1, and IJ inches 

 focus are sufficient. 



245. To assist the student in deierminmff or ascertaining the name of a plant be- 

 longing to a Flora, analytical tables should be prefixed to the Orders, Gtenera, and 

 Species. These tables should be so constructed as to contain, under each bracket, or 

 equally indented, two (rarely three or more) alternatives as nearly as possible contradic- 

 tory or incompatible with each other, each alternative referring to another bracket, or 

 having under it another pair of alternatives further indented. The student having a 

 plant to determiue, wUl first take the general table of Natural Orders, and examining 

 his plant at each step to see which alternative agrees with it, wUl be led on to the 

 Order to which it belongs, he wiE then compare it with the detailed character of the 

 Order given in the text. If it agrees, he will follow the same course with the table of 

 the genera of that Order, and again with the table of species of the genus. But in 

 each case, if he finds that his plant does not agree with the detailed description of the 

 genus or species to which he has thus been referred, he must revert to the beginning 

 and careftdly go through every step of the investigation before he can be satisfied. A 

 fresh examination of his specimen, or of others of the same plant, a critical considera- 

 tion of the meaning of every expression in the characters given, may lead him to detect 

 some mmute pomt overlooked or mistaken, and put hhu into the right way. Species 

 vary within limits which it is often very difficult to express in words, and it proves 

 often nnpossible', m framing these analytical tables, so to divide the genera and species 

 that those which come under one alternative should absolutely exclude the others' 

 In such .doubtful cases both alternatives must be tried before the student can come to 

 the conclusion that his plant is not contained in the Flora, or that it is erroneously 

 described. ' 



246. In those Floras where analytical tables are not given, the student is usually 

 guided to the most important or prominent characters of each genus or species, either 

 by a general summary prefixed to the genera of an Order or to the species of the 

 genus for aU such genera or species j or by a special summary immediately preceding 

 the detaaed description of each genus or species. In the latter case this summary 5 

 caUed a diognosM Or sometimes the important characters are only indicated by 

 italicizmg them m the detailed description. ' 



247. It may also happen that the specimen gathered may present some occasional 

 or accidental anomahes peculiar to that single one, or to a very few individuals, which 

 may prevent the species fi;om bemg at once recognized by its technical charactelrs. It 

 ^n{t^fv»ff ;^ t ^J"'""^ out a few of these anomalies which the botanist may be 

 most likely to meet with For this purpose we may divide them into two classes, 4. : 



sea^o^rlMrffM?nfl 7"" f "^f i""- Particularly at considerable elevations above the 



p"ant "■'• ™ P™PO=^tio" *<> the stature and foliage of the 



moS todU to°^crZ«Tf f ^ '"^ accompanied by richness of soil and sufiicient 



A hot climate and dry situation tend to increase the hairs, prickles and other nro- 



