Natural Habitats and Nativeness. 95 
In relation to man as a predominating factor in the botanical 
problem all we have to set ourselves to disentangle is, ‘“‘ what is 
_ permanent, and what is transitory.” The former is natural, 
the latter accidental, semi-alien, or alien. No other criterion 
appears to be possible. It has the advantage of being simple 
and practical. It may be difficult to say whether a given 
_ species is “ native, denizen, colonist or casual,’ under a certain 
environment, but it is easy enough to ascertain whether it is 
permanent or transitory. It isnot difficult to demonstrate whether 
a plant is found in the majority of fitting situations, or whether it 
is peculiar to one locality, or at most a few under suspicious 
_ circumstances, under the same conditions of growth. 
f To help in this respect, and to escape from the difficulties 
_and perplexities of the Watsonian system of terminology, I 
propose to class all species into various categories, as they stand 
in an intimate or more distant relation to man and his under- 
takings. Their position in a category or categories will at once 
settle their status. Samples only can be given here. Followers 
(1) of man, (2) of cultivation, (3) of commerce. Frequenters (1) 
of broken ground, (2) of waste ground, (3) of pasture, (4) of 
meadow, (5) of woodland, (6) of road-side hedges, (7) of field 
hedges, (9) of lakes, (10) of ditches, &c., are much more simply 
applied, even though the phase lacks the sweet simplicity of the 
Watsonian word. Both should contain a distinct idea, or set of 
‘circumstances, unfortunately, in practice, this is what Watson 
words do not express. 
___ Now as regards application. Thlaspi arvense is at best an 
“uncertain “ Follower (2) of cultivation ” in Lincolnshire. It was 
“introduced into Cadney parish with seed wheat some 40 years 
ago. Happening on a soil—dry arable Peat mixed with Chalky 
Boulder Clay—that exactly suited its requirements, it has 
remained till to day. It is confined as a semi-permanent species 
‘to the narrow band of mixed soil where it was originally sown. 
This spring while analysing the flora, which gradually and 
through many changes, wins back the bare patches the stone 
heaps leave by the road side after the metal has been used on the 
t permanent way, I came across two isolated plants of T. avvense 
