APRIL, 1903. | THE ORCHID REVIEW. 123 
when they enter the micropyle of the ovule, and unite with the contents of 
egg-cell, this latter constituting the act of fertilisation, after which alone the 
ovule can develop into a perfect seed. But if an Orchid flower be examined 
at the same stage, the ovarian cavity and ovules will be found in quite a 
rudimentary stage, and if not pollinated they will progress no further, at 
length falling off in the same stage. But when pollinated a rapid change 
takes place. The column begins to swell, and its wings to curve inwards. 
over the column, while the segments quickly begin to fade or change colour. 
This fact is well known to cultivators, and efforts are made to keep bees out 
of the houses, as they spoil the flowers by pollinating them. 
The act of pollination applies a stimulus to the ovary, causing it to- 
swell, and at the same time the ovules develop, and it is only after develop- 
ment that fertilisation can take place. In the case of Cattleya Mossiz 
the whole process has been carefully worked out by Messrs. Veitch, who 
by a series of experiments ascertained that fertilisation does not take place 
until a period of from 75 to go days after pollination. The process is briefly 
as follows:—A few hours after pollination the floral segments become 
flaccid, and show signs of withering. In a couple of days the pollinia are 
seen to be disintegrating, forming, with the viscid secretion from the stigma, 
a gelatinous mass that quite fills up the stigmatic cavity. At the same time 
the pollen tubes have commenced to grow, and in eight days they have 
reached the base of the column, being found in vast numbers among the 
cells of the conducting tissue. At the end of a month the ovary has become 
considerably enlarged, and the placentz and ovules are beginning to assume 
a definite form, while the pollen tubes are pushing downwards along the 
sides of the placentze and among the ovules. In two months, though the 
pollen tubes are present in countless numbers, and have even reached 
the base of the ovary, the ovules are not yet developed, but soon afterwards. 
they rapidly undergo a change of form, and at the end of about three 
months the long looked for event takes places. The pollen tubes now 
enter the micropyle of the ovule, and fertilisation of the egg-cell takes place- 
It is noteworthy that before this event takes place the ovary has 
developed from a terete body, less than a quarter of an inch in diameter,. 
toa six-angled one, more than seven times as broad, entirely through the 
stimulus given by the act of pollination, and the subsequent growth of the 
pollen tubes, which enables one to realise to some extent the reason why a 
capsule may go off after making considerable progress, or even contain 
no good seed. There is reason to believe that the period required for 
the development of the pollen tubes and ovules varies somewhat in 
different Orchids, and this may possibly represent one cause of failure 
when very distinct species are intercrossed. 
(To be continued.) 
