153
ILLUSTRATIONS OF INDIAN EOTANY.
that his collection contains several not in Wallich's list, and Mr. Arnott writes me that he has recently described sixteen new ones from Ceylon. To these last, my excursions on the Courtallum and Shevagerry hills have added about as many more. Of the Courtallum ones, those only of which drawings were made, are introduced into this paper; not having, either specimens or sufficiently perfect notes, to enable me to define the rest.
It is a curious, and to me an inexplicable fact, that a genus so strikingly Indian, and associating such a host of species, should have been so little known to Roxburgh. He only describes three in his Flora, though I am sure I speak within bounds, when I assert that the countries, whence he derived the materials for his work, will be found to present an assemblage of not fewer than one hundred species. It is no doubt an eminently alpine genus, delighting in a cool and moist climate ; hence it is unknown on the plains of Coromandel, though not unfrequent in Mysore, but, so far as I have seen, only abounding, in the Peninsula, on the higher hills participating in the western monsoon, which enjoy, during the hot months, a moderate range of temperature, with a very humid atmosphere. Some, (how many is not yet known,) are found during the monsoon on the Malabar coast, little elevated above the level of the sea, but, except in Tanjore, I have not seen one of the order on the plains eastward of the ghauts, beyond the influence of that monsoon: and the only one found there, is Hijdrocera trijiora, which grows, but is not common, in its ditches and swampy grounds, during the cool season, and is the only place where I have yet seen it.
This peculiarity of distribution may account for his not having met with Peninsular species, as he was but little in the southern provinces, and perhaps they are not found in the eastern range of the northern ghauts : but, twenty-two of the forty-seven species named by Wallich, are from Silhet, Pundooa and Nepaul, from all of which places Roxburgh procured plants, and one of the three he describes is from Silhet. A moist climate and moderate temperature are the circumstances most favourable, if not indispensable, to their production ; hence we find twenty two, of the remaining twenty-five species named by Wallich, natives of the Peninsula, but confined to the ghauts and Mysore where these contingercies meet. This fact was first noticed by Mr. Royle, who, after remarking the nearly equal division of the forty-seven species between the frontier mountains of Bengal and the Peninsula, adds, " a singular equality of numbers, seeing that we have hitherto found Peninsular and South of India genera confined to the base of the mountains, and if found existing on them, generally only as single species; but here we have them in equal numbers, some of them extending to an elevation of seven thousand feet.
" This anomaly can only be explained, and a stronger fact cannot be adduced in its confirmation, than that the moisture and moderate temperature of the rainy season in the hills (for it is at this season only that they are found) is as favourable to their growth as the hear and moisture of the Peninsula. I have never met with any in the plains of India ; but have heard from travellers that they are abundant in Central India, whence we may expect some new species, as well as from thp Neilgherries."
The facts which I have mentioned regarding the distribution of the Peninsular species, go to pi-ove, that heat and moisture are not the circumstances most favourable to their production here, but moisture combined with a moderate but equal temperature. At Courtallum for example, whence I have eleven or twelve species, they most abound in shady places on the tops of the hills, with a mean temperature during the season of their greatest perfection, not exceeding 70°, if so much. At Shevagerry, about fifty miles north of Courtallum, 1 found five, out of seven species, on the highest tops of the mountains ; none of the five u'«tder 4,000 feet, and three of them above 4,500 feet of elevation ; the mean temperature, as deduced from twenty observations, continued through four days, at an elevation of 4,100 feet, being 65° of Fahrenheit's scale. The two found at a lower elevation, were both either growing in the gravelly beds of streams, or immediately on their banks ; the temperature of which was ascertained to be 65°, while that of the air at noon was only about 75 a , a temperature, I presume, but little above that in which they delight on the Bengal frontiers. There is one other point, respecting the effect of climate on plants of this genus, to which I wish to call attention, as it may ultimately prove useful to any one who may again attempt to subdivide it, and is, in the mean time, in a physiological point of view, exceedingly curious. It is, that most of the species from the colder regions of the Himalaya mountains, correspond with the European I. noli tangpie, in the form- and dehiscence of their capsule, that is, they split from the base, rolling the segments toward*
