144 THE ORCHID REVIEW. 
genera, and groups of higher rank. These considerations help us to 
understandjthe difficulty in certain cases of defining the limits of species, 
and also why the most closely allied plants occur in different localities. 
Two or more allied species may be found growing together in one 
spot, but generally speaking they have nearer relations elsewhere, and 
even when this is not the case there are strong reasons for believing that 
they originated separately, and were afterwards brought together. Probably 
no instances could be found of two species occupying absolutely identical 
geographical areas. Their boundaries are hardly ever conterminous, of, 
in other words, they may grow together in certain localities, but there are 
others where they grow separately, or in different combinations. These 
several considerations help us materially to understand the phenomena of 
natural hybridism. 
Natural hybrids only originate where two or more allied species grow 
in sufficient proximity to each other for the pollen of one species to reach 
the stigma of the other. In the case of Orchids we know how this is 
effected by insect agency. The species must also have retained theif 
congenital affinity, or, in other words, be capable of hybridising together. 
Wherever these conditions obtain, natural hybrids may occur. In most 
cases they are found growing with the parent species. It may not always 
be the case, for the light seeds of Orchids may be carried some distance, 
though we have very little evidence of its taking place om any extensive 
scale. Were it otherwise the species would be more generally diffused. 
And in any case uncrossed seed would be likely to be carried to the same 
distance, and to germinate, if placed under favourable conditions. 
Natural hybrids, like those obtained artificially, almost invariably show 
a distinct combination of the characters of the two parent species, which 
may usually be traced on careful examination. Sometimes the character 
of one parent preponderate over those of the other, and it becomes 4 . 
difficult case to identify the second one, but generally speaking hybn 
may be said to bear the stamp of their origin in their faces. . 
Another fact respecting them is that, compared with the pa 
they are very rare. Sometimes a single individual appears in an imp? 3 
tion, and is not recognised until it flowers; in other cases there may : 
several. In a few cases the individuals are numerous, because the os 
has been effected over and over again, and large importations of P 
have been made. 
it has bee? 
Again, they are usually very variable. From the very first it aia 
observed that it was a rare occurrence for any two of them to be they 
etimes 
though apparently derived from the same two species, and som 
have received different names. This variability is well kn ae 
case of artificial hybrids. 
(Zo be continued.) 
