JulU', 1913.I 
'IHI-: ORCHID WORIJ). 
199 
placed upon the stigma. The reason why the 
few attempts so far made in this direction 
have more often than not ended ni faikire must 
now be considered. 
Cattleya labiata when crossed with Cattleya 
Hardyana (gigas x aurea) produces seedhngs 
inheriting the characters of all three species, 
because each single pollen grain from the 
Hardyana contains in a fused state the 
characters of both gigas and aurea. But if 
C. labiata is fertilised with two pollen masses, 
one of which comes from gigas and the other 
from aurea, the resulting seedlings are either 
C. amabihs (labiata x gigas) or C. Fabia 
(labiata x aurea), just in the same way as 
though two distinct flowers of labiata had been 
pollinated each with only one kind of pollen. 
There is no possibility of obtaining a hybrid 
similar to labiata x Hardyana, for the simple 
reason that only one pollen grain, either from 
the gigas or aurea, is able to fertilise an ovule 
of the labiata. 
In using two or more diverse pollen masses 
there are certain factors necessary to ensure 
success, and, unfortunately, these are not 
entirely under our control. In the first place, 
it is not advisable to put the whole of both 
pollen masses on to the stigma, for, as 
previously mentioned, the unusual size of the 
mass may cause the whole to be rejected. 
The safest way is to use only sufficient 
portions of each that will make the whole of 
normal size. Thus if two species are used as 
pollen parents, only one-half of each pollen 
mass should be used ; and, if four male 
parents, then one quarter of each will prove 
sufficient. 
Secondly, the growth of the pollen grains 
through the column and amongst the ovules is 
a factor of which we have no control. It 
appears impossible for the short growing 
pollen grains of Sophronitis grandiflora to 
grow down the whole length of the long style 
possessed by Brassavola Digbyana ; they 
grow to a certain length, but never sufficiently 
far to reach the ovules and effect fertilisation. 
Therefore, in the use of mixed pollen, the 
inability of one kind to reach the ovules might 
be a cause of the failure to produce our desired 
VOL. III. 
result of obtaining two different hybrids from 
the same seed pod. It will be readily seen 
that the only pollen to take effect would be the 
one capable of growing sufficiently in length 
to reach the ovules. 
Thirdly, the rate at which the pollen grains 
grow down the column into the ovary needs 
consideration, for it is fairly certain that all 
pollen grains are not equally rapid in their 
growth. It is known that the number of 
separate ovules and pollen grains can only be 
reckoned in tens or hundreds of thousands, 
but for simplicity let us assume that the 
number of ovules is only ten. If now an 
equal number of pollen grains be used there 
will be one to fertilise each ovule ; but suppose 
two kinds of pollen masses, each consisting of 
ten grains, are placed on the stigma, then it 
is quite possible that one kind may be of much 
quicker growth than the other, and these by 
arriving first in the ovary will fertilise all the 
ovules before the second or slower-growing 
kind arrives. It is at once obvious that the 
latter can have no influence whatever. But if 
only five pollen grains from each are placed on 
the stigma there is every possibility that each 
one will in due course meet with an unfertilised 
ovule. Thus we see the need of using a 
portion only of each pollen mass. 
Fourthly, the passage of the pollen down 
the style and into the ovary must also be 
considered. Each pollen grain grows down 
the central loose tissue of the style in the form 
of an elongated cell, generally known as the 
pollen tube. This process is brought about by 
the action of enzymes, or dissolving material, 
contained in the tube, which enables it to bore 
its way down the style and eventually reach an 
ovule. A second object of these enzymes is 
to abstract nutritive substance from the 
surrounding material in order to nourish the 
growing pollen tube. It will, therefore, be 
seen how much really depends on the effec- 
tiveness of the enz)'mes, for if they are unable 
to perform their function it is impossible for 
the pollen grains to reach the ovules. 
It is extremely difficult, one might almost 
say impossible, to hybridise Odontoglossum 
crispum with the pollen of Odontoglossum 
?6 
