XXXVl INTUODUCTION. 



244. For dissecting and examining flowers iii 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 convenient to have a mounted lens or simple microscope, with a stage holding 

 a glass plate, upon which the flowers may be laid ; and a pau' 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 ovaiy. A compound microscope is rarely necessary, except in cryptogamic botany 

 and vegetable anatomy. For the simple microscope, lenses of i, |, 1, and 1| inches 

 focus are sufiicient. 



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

 longing to a Flora, analytical tables should be prefixed to the Orders, Genera, 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 determine, will first take the general table of Natural Orders, and examining 

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

 Order to which it belongs, he will 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. Bvit 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 i-eferred, he must revert to the beginnmg 

 and carefully 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 minute point overlooked or mistaken, and put liim into the right way. Species 

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

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

 that those which come xmder one alternative should absolutely exclude tlie 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 all such genera or species ; or by a special summary immediately preceding 

 the detailed description of each genus or species. In the latter case this summary is 

 called a diagnosis. Or sometimes the important characters are only indicated by 

 italicizing them in 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 from being at once recognized by its technical characters. It 

 may be useful here to point 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, viz. : 



1. Aberrations from the ordinary type or appearance of a species for which some 

 general cause may he assigned. 



A bright, light, and open situation, particularly at considerable elevations above the 

 sea, or at high latitudes, without too much wet or drought, tends to increase the size 

 and heighten the colour of flowers, in proportion to the statm-e and fohage of the 

 plant. 



Shade, on the contrary, especially if accompanied by richness of soil and sufficient 

 moisture, tends to increase the foliage and draw up the stem, but to diminish the num- 

 ber, size, and colour of the flowers. 



A hot climate and ch-y situation tend to increase the hairs, prickles, and other pro- 

 ductions of the epidermis, to shorten and stiffen the branches, rendering thorny plants 

 yet more spinous. Moisture in a rich soil has a contrary effect. 



The neighbom'hood of the sea, or a saline soil or atmosphere, imparts a thicker and 

 more succulent consistence to the fohage and almost every part of the plant, and ap- 



