CHAP. VIII. 
FERTILISATION. 
343 
Mr. Bauer, and the general structure of the order, seem at 
variance with the probability of actual contact being necessary ; 
and, as Brown is obliged to have recourse to the supposition 
that the pollen of many of these plants must be actually 
carried by insects from the boxes in which it is naturally 
locked up, it would seem that the mode of fertilisation in 
Orchidaceae is still unsettled. I must particularly remark 
that the agency of insects, to which Brown has recourse in 
order to make out his case, seems to be at variance with his 
supposition that the insect forms, which in Ophrys are so 
striking, and which, he says, resemble the insects of the coun- 
tries in which the plants are found, “ are intended rather to 
repel than to attract.” But although such arguments are 
objectionable, it is, nevertheless, now certain that Orchidaceae 
require that contact between their pollen and stigma should 
take place in order to insure fertilisation. This has been 
shown by Professor Morren, and has now become in gardens 
a matter of notoriety. 
The most interesting and precise accounts of the process 
of impregnation yet given are those by Mr. Griffith, in the 
Tram, of the Linn. Soc, vol. xviii., with numerous explana- 
tory plates. This excellent observer describes the impregna- 
tion of the ovulum of Santalum album as taking place by a 
pollen tube first coming in contact with the sac of the amnios, 
with which it becomes blended, without perforating the 
membrane. The molecular matter has at this time lost its 
locomotivity, and becomes aggregated into a grumous line 
reaching from the apex of the sac to its base. Then a glo- 
bular vesicle, containing mobile granules, appears at the apex 
of the sac, in communication with the grumous molecular line. 
About the same time a distention of the base of the sac 
occurs, and a central cell is formed in it ; by degrees the space 
intervening between the latter and the apex of the sac 
becomes cellular, and changes to a suspemor, having an 
embryo at that end which is next the base of the sac. 
In Loranthus and Viscum the ovulum is not formed till some 
time after the stigma is impregnated by the pollen. Subse- 
quently to that event, a slender sphacelated line, not pre- 
viously discernible, reaches from the stigma to the interior of 
z 4 
