216 NOTICES OF BOOKS. 
words inappreciable differences in colour, smell, flavour, etc., yet in 
horticulture the methodical distinction of varieties, however vague and 
uncertain, is often of considerable importance. But we are daily more 
and more threatened with invasions into the field of botany of similar 
principles. Species which, owing to their wide geographical range and 
facility of accommodating themselves to a number of different climates, 
seasons, soils, and aspects, show great diversity in their outward appear- 
ance, have been considered as genera; and any appreciable differences, 
not only in different individuals but in fragmentary specimens, have been 
regarded as distinguishing species. Instances could be named where 
two or three genera and twenty or thirty species have been carved out 
of a single Linnean species, which an unprejudiced review of numerous 
specimens from a great variety of localities compels us to return to. 
This is more especially the case with the weeds of cultivation, with | 
maritime, aquatic, and amphibious plants, and with those genera and 
natural orders where the type of the floral organs is much reduced, 
such as Pistia, Callitriche, Chara, Ferns, and Glumaceous plants. 
The Graminee have been peculiarly unfortunate as to their specific 
demarcation. With a great general similarity of habit, this extensive 
family presents a wonderful variety in the modifications of the floral 
. parts. This circumstance, together with the great reduction these 
organs have undergone from the more regular types of the higher Mo- 
-nocotyledonous Orders, has directed to Graminee the special attention 
. of many of the greatest botanists, as well as of a host of minor dabblers 
in the science. Speculations without number have been put forth on 
their typical structure, a large proportion of species have been analysed 
and described with the greatest minuteness, and a still larger mass of 
orms haye been published with loose and incomplete diagnoses ; but we 
have as yet had no experienced botanist, with true philosophical views, 
vho has taken the trouble to go through the chaotic mass and reduce 
it to manageable order. Trinius and Nees von Esenbeck have done the 
most towards it; but Trinius’s materials were insufficient, and he did 
not live to complete his work. Nees von Esenbeck's labours show the 
greatest knowledge of the subject, and if we do not always agree with 
him in the number of species he admits, still the forms he describes are 
the least appreciable varieties, and his observations are accurate; but 
also has given up the science without having completed any general 
i the Order. Kunth had studied the family well, and described 
