HUGHLI-HOWRAH AND THE 24-PERGUNNAHS. 
167 
not only belong to this class but that only appear in our districts 
-owing to repeated introductions, and could no more survive under 
the conditions prevalent during the south-west monsoon that could 
many of the cold-weather crops. But, as already explained, there is 
one point of view from which every species growing on the deltaic 
alluvium is an introduced species, and nothing can be learned from 
an examination of the plants with reference to this question that 
could not be better learned elsewhere and by other means. When, 
however, it is a question of the species known to be natives of 
countries other than India, a brief examination of these repays the 
trouble. The list includes the following :—Argemone mexicana, 
American; Senebiera pinnatifida, Mediterranean; Malachra 
capitata, American ; Crotalaria patula, Indo-Chinese ; Cassia occi- 
dentalism American ; Mimosa pudica, American ; Ageratum conyzoi - 
desy American ; Xanthium spinosum, Mediterranean ; Lagascea 
mollisy American; Synedrella nodiflora, American; Tridax procum- 
bent, American ; Evolvulus nummular if oli us, American ; Nicotiana 
plumbagini folia , American ; Herpestis chameedroides , American ; 
Scoparia dulcis , American ; Peperomia pellucida , American ; 
Euphorbia graminea, American ; Croton sparsiflorus , American ; 
Jatropha gossypifolia , American ; Typhonium inopinatum , Indo- 
Chinese ; Paspalum conjugatum , American. 
Of these species one-tenth are of Mediterranean and one-tenth 
of Indo-Chinese origin, while four-fifths are originally American ; 
these American species include in Ageratum conyzoides , Tridax 
procumbens. Cassia occidentalis , Scoparia dulcisy Peperomia pellu - 
ciaa, some of the very commonest species in the neighbourhood of 
Calcutta. 
There is, however, another very interesting feature in connection 
with these introduced weeds. Their presence indicates a process 
that is steadily going on ; yeir by year new species become added 
to the flora of the neighbourhood of Calcutta. Of the species in the 
list we know that Argemone mexicana , Argeratum conyzoides , Cassia 
occidentalisy Mimosa pudica , Tridax procumbens were already 
members of the flora in 1795. But we also know that as late as 
1814 none of the others were yet introduced and naturalised. By 
1845, however, Scoparia dulcis , Senebiera pinnatifiday Lagascea 
mollis , Malachra capitata , Nicotiana plumbagini folia had all 
become established. By 1885 Evolvulus nu?nmularius ) Crotalaria 
patula , Jatropha gossypifolia , Peperomia pellucida, Paspalum 
conjugatun, Synedr ella nodiflora and Euphorbia graminea had 
become established as members of the Calcutta flora. The period 
