100 JOURNAL OF THE ROYAL HORTICULTURAL SOCIhVrY. 



and it is by no means improbable that the experimenter of to-morrow 

 may be able to induce plants to develop seed by chemical or mechanical 

 stimulation similar to that which, as we have seen, has proved effective 

 in the lower animals. 



It is possible, however, that this experiment has been performed 

 already by Nature herself in the case of Zygopetalum Mackayi. 



So far as I know, this Orchid does not produce seed unless it be 

 pollinated. When it is pollinated with the pollen of certain other 

 species, i.e. Odontoglossum cris'pum, it produces good seed, but to use 

 the words of my friend Mr. O'Brien, the extent of whose knowledge 

 of Orchids is rivalled only by the generosity with which he imparts it, 

 " the progeny still remain Zygopetalum Mackayi, with only sufficient 

 suggestion of a difference in the flowers to prove that the cross has 

 been made. This cross has been made several times with the same 

 result, and other combinations have given rise also to the same 

 progeny." As a contribution to the explanation of this remarkable 

 behaviour I would offer the following suggestions : First, that the 

 offspring of the cross Zygopetalum Mackayi by Odontoglossum crispum 

 are pure Zygopetalum Mackayi; second, that the effect of the pollen 

 of the Odontoglossum is that of Bataillon's needle; the pollen or 

 pollen tubes, although they make no material contribution tO' the egg- 

 cell, give the fertilization-stimulus without which the egg-cells of 

 Zygopetalum are unable to develop. Given this stimulus the egg-cells 

 develop parthenogenetically. I am willing to admit, however, that the 

 behaviour- of this remarkable plant may be yet more subtle than this, 

 but into a discussion of these subtleties this is not the place to enter. 

 The suggestion just offered — that the only part or lot that Odonto- 

 glossum crispum has in the fertilization of Zygopetalum Mackayi is in 

 providing a fertilization-stimulus — may appear far-fetched to any but 

 those acquainted practically with the ways of Orchids. 



Those who work with more torpid, less highly-strung plants may be 

 disposed to ask. What justification is there for the suggestion that the 

 pollen of Odontoglossum crispum deposited in the stigmatic surface of 

 Zygopetalum Mackayi may, whilst failing to effect fertilization, yet 

 act as a stimulus to the parthenogenetic development of the egg-celis of 

 that plant? 



But the man who works among Orchids will not be disposed to be 

 so sceptical. He is aware of the fact that a fly or even specks of dust 

 settling on the stigma may provoke changes in the flower similar to 

 those which follow on pollination. A striking illustration is provided 

 by the specimens of Odontoglossum crispum, bearing both normal 

 white and canary-yellow flowers, which are frequently sent to the 

 Gardeners' Chronicle by growers who want to know whether the 

 yellow flowers represent a sport. As is known to experienced 

 orchidists the latter colour is assumed by the flower as a consequence 

 of pollination. It may also be induced, as the specimens show, by a 

 contact-stimulus set up by dust or grit falling on the stigma. Having 

 in view such facts as these and also their application to the case cf 



