NATURAL HISTORY OF THE BANKS OF THE TAY. 59 
be mentioned should be really thus classed is open to question. 
It may be that they are confined to the upper districts, or are more 
abundant there, merely because the physical conditions do not suit 
them in the tidal district. Examples are several species of Hieradum^ 
Vida sylvatica, Meuvi athaniandcum^ and probably others. 
In this connection the abundance of Thalictrum minus in the 
upper districts, and its absence in the greater part of the tidal district, 
must not be overlooked. 
Regarding the upper districts it may be at once said that their 
floras do not differ to any material extent. As might be expected, we 
find a thinning out of certain weeds of cultivation, such as the 
poppies and fumitories, as we ascend the river, but most of the other 
differences in the floras arise either from the inexplicable restrictions 
in the range of some local plants, or in the physiographical conditions 
of the banks. The presence of trap dykes, conglomerate beds, and 
wet sandstone rocks has an effect in localising certain species, but 
to all intents and purposes the main features of the flora are the 
same. Still, however, a careful analysis reveals the fact that some 
plants, which are more or less abundant in the lower part of the 
Strathmore district, become much rarer, or disappear altogether, in 
the upper parts of the Highland district. We have not sufficient 
statistics to enable us to speak very definitely on this point, but are 
inclined to think that Hypericum perforatum and Kiiautia arvensis 
may be cited as examples, as also Chcerophyllum teinulum and 
Caucalis aniJiriscus. The cause of this disappearance of certain 
species is probably connected with the temperature, but a great deal 
has yet to be learned on this subject. 
A brief recapitulation may be useful. 
1. The flora of the tidal district shows greater differences from 
the floras of the two other districts than they do from each other. 
2. The characteristics of the flora of the tidal district are the 
presence of maritime and “temperature” plants, and the absence 
of alpine and upland species. 
3. The differences between the floras of the Strathmore and 
Highland districts are not marked, and consist chiefly in the less 
abundance or in the disappearance of certain plants as the river is 
ascended. 
In conclusion, I may say that the number of species of flowering 
plants and ferns, native or introduced, observed on the ground to 
which our researches have been limited, amounts to about 486.* 
* Further information regarding the flowering plants of the district will be 
found in the “Flora of Perthshire,” by the same author, which is at present in 
the press. 
