358 
THE TROPICAL AGRICULTURIST. [November i, 1888. 
PLANT- LIFE. 
(From Mr. W. T. Thiselton Dyer's address to the 
Biological Section of the British Association at Bath.) 
Geographical Distbibution. 
Perhaps those which are yielded by the study of 
geographical distribution are of the most general in- 
terest. The mantle of vegetation which covers the 
surface of the earth, if only we could rightly UDravel 
its texture, would tell us a good deal about geological 
history. The study of geographical distribution, right- 
ly handled, affords an independent line of attack 
upon the problem of the past distribution of land 
and sea. Here, however, we are embarassed by the 
enormous amount of work which has yet to be accom- 
plished. And unfortunately this is not of a kind which 
can be indefinitely postponed. The old terrestrial order 
is fast passing away before our eyes. Everywhere 
the primitive vegetation is disappearing as more and 
more of the earth's surface is brought into cultivation, 
or at any rate, denuded of its forests. A good deal, 
however, has been done. We owe to the indomitable 
industry of Mr. Bentham and of Sir Ferdinand Mul- 
ler a comprehensive flora of Australia, the first large 
area of tbe earth's surface of which the vegetation has 
been completely worked out. Sir Joseph Hooker, in 
his retirement, has pushed on within sight of com- 
pletion the enormous work of describing so much of 
the vast Indo-Malayan flora as is comprised within 
British possessions. To the Dutch botanists we owe 
a tolerably complete account of the Malayan flora 
proper. But new Guinea still remains botaDically a 
terra incognita, and till within the labt year or two 
tbe flora of China has been an absolute blank to 
us. A committee of the British Association has, with 
the aid of a small grant of money, taken in hand 
the task of gathering up the scanty data which are 
available in herbaria and elsewhere. This has stimul- 
ated European residents in China to collect more 
material, and the fine collections which are now being 
rapidly poured in upon us will, if they do not over- 
whelm us by their very magnitude, go a long way 
in supplying data for a tentative discussion of the re- 
lations of the Chinese flora to that of the rest of 
Asia. I do not doubt that this will in turn explain 
a good deal that is anomalous in the distribution of 
plants in India. The work of the committee has been 
practically limited to Central and Eastern China. From 
the west, in Yunnan, the French botanists have re- 
ceived even more surprising collections, and these 
supplement our own work in the most fortunate 
manner. I have only to add for Asia Boissier's Flora 
Oriental™, which practically includes the Mediter- 
ranean basin. But I must not omit the invaluable 
report of Brigade-Surgeon Aitchison on the collections 
made by him during the Afghan Delimitation Ex- 
pedition. This has given an important insight into 
the vegetation of a region which had never previously- 
been adequately examined. Nor must I forget the 
recent publication of the masterly report by Professor 
Bayley-Balfour on the plants collected by himself 
and Schweinfourth in Socotra, an island with which 
the ancient Egyptians traded, but the singularly 
anomalous flora oi' which was almost wholly unknown 
up to our time. The flora of Africa has been at 
present but imperfectly worked up, but the materials 
have been so far discussed as to afford a tolerably 
r met theory of its relations. The harvest from 
Mr. Johnston's expedition to Kilima-Njaro was not 
as rich as might have been hoped. Still it was suffi- 
cii nt to confirm the conclusions at which Sir Joseph 
Hooker hail arrived, on very slender data, as to the 
Irelal 'one of t he high-level vegotation of Africa general- 
ly. The flora of Madagascar, investigated by Mr. 
Baker, is perhaps at the moment the most interest- 
iiiK problem which Africa presents to the botanists. 
The flora as a whole presents a large proportion of 
endemic genera and species, pointing to isolation 
from a very at cient date. The tropical element is, 
however, closely allh d to that of Tropical Africa and 
of tbe Mascerene Islands, and there is a small infusion 
of Asiatic types Which do not extent to Africa. The 
high-level flora, on the other hand, exhibits an even 
closer affinity with the temperate flora, the ruins of 
which are scattered over the mountainous regions of 
Central Africa, and which survives in its greatest 
concentration at the Cape. The American botanists 
at Harvard are still systematically carrying on the 
work of Torrey and Gray in the elaboration of the 
flora of Northern America. The Russims are, on their 
part, continually adding to our knowledge of the flora 
of Northern aud Central Asia. The whole flora of 
the north temperate zone can only be regarded sub- 
stantially as one. The identity diminishes southwards, 
and increases in the case of the aictic and alpine 
regions. A collection of plants brought us from high 
levels in Corea by Mr. Jamrs might, as regards a 
large proportion of the species, have been gathered 
on one of our own Scotch hills. We owe to the 
munificence of two English men of science the organis- 
ation of an extensive examination of the flora and 
fauna of Central America and the publication of the 
results. I am happy to say that tbe botanical por- 
tion, which has been elaborated at Kew, is all but 
finished. In South America I must content myself 
with referring to the great Flora Brasiliensis, com- 
menced by Martius half a century ago, aud still slowly 
progressing under the editorship of Professor Uibau 
at Berlin. Ihe travels of Mr. Ball in South America 
have led him to the detection of some very interesting 
problems. The enormous pluvial denudation of the 
ancient portions of the continent has led to the gradu il 
blending off the flora of different levels with sufficient 
slowness to permit of adaptive changes in the process. 
The tropical flora of Brazil, therefore, presents an 
admixture of modilied temperate types, which gives 
to the whole a peculiar character not met with to the 
same degree in the tropics of the whole world. On 
tbe other hand, the c miparn'ively recent elevation of 
the southern portiou of the continent accounts, in 
Mr. Ball's eyes, for tbe singular proverty of its tiura, 
which we may regard iodeed as .still in progress of 
development. 
The Botany of the " Challeuger" Expedition which 
was also elaborated at Kew, brought for the first time 
iuto one view all the avilable facts as to the floras 
of the older oceanic islands. To this was added a 
discussion of the orgin of the more recent floras of 
the islands of tbe Western Pacific, based upon material 
carefully collected by Profe.-sor Mosely and .supple- 
mented by the notes and specimens accumulated with 
much judgment by Dr. Guppy. Fur the first time 
we were euabled to get some idea how a tropical 
island was furuishe I with plauts, aud "to discrimi- 
nate the littoral element clue to the action of oceanic 
currents from the interior forest, almost wholly due 
to frugivorous birds. The recent examination of 
Christmas Island by the English Admiralty has showu_ 
the process of island flora-making in another stagej 
The plants collected by Mr. Lister prove, as -migh 
be expected, to be closely allied to those of Java. 
But the effect of isolation has begun to tell ; aud I 
learn from my colleague, Professor Oliver, that the 
plants from Christmas Ibland cannot be for the most 
part exactly matched with their congeners from Java, 
but yet do not differ sufficiently to be specifically 
distinguished. We have here, therefore, it appears to 
me, a manifest case of nascent species.— Gardeners' 
Chronicle. 

Heated Borders in the Open Air.— I send you a 
Pine-apple, aud some Peach and Nectarine fruits 
ripened in my "Hypocaust," or heated earth garden, 
in the open air. One Peach aud one Nectarine, 
supplied by Mr. .Rivers for the purpose, with the fruit 
well set, were plunged in the hot earth, and the 
Piue-apple, a small-fruiting sucker, was planted right 
out. This was in the first part of June. The peach 
and Nectarine never suffered a check and are now 
in healthy aud luxuriant foliage. The fruits I send 
were attacked by slugs and so dropped. The Pine 
grew strougly, and the fruit, about the size of a green 
Walnut when put out, had become yellow and per- 
haps ripe, ten days before.— R. Trevor Clakke.— 
Gardeners' Chronicle. 
