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JOURNAL OF T?TE ROYAL HORTTCH LTllRAL SOCIETY. 



unless the pollen used be alive and that of the species itself, the 

 stigma lobes, after a longer or shorter interval, separate once again 

 from one another. That is to say, the shrunk cells re-absorb water, 

 return to their original size, and push the lower surface outward and 

 downward. 



But if a good load of pollen of Mimulus cardinalis be put on the 

 stigma of a flower of that plant, the stigma lobes close, and open no 

 more. Here we have an illustration of the second of our three results 

 of pollination — namely, that of intoxication. I do not suggest that the 

 failure to re-open means that the stigma of Mimulus is plunged in a 

 drunken sleep ; but that the failure of the lobes to separate is due to the 

 fact that the pollen excretes a poisonous substance which brings about 

 a disorganization of some of the cells of the stigma, as a result of which 

 they can no longer absorb water, and hence cannot press back the 

 appressed lobes. That this explanation is correct is demonstrated by 

 the fact that a watery extract of the pollen suffices to bring about 

 both a closure and a failure to re-open : the former by setting up a 

 contact stimulus; the latter by poisoning certain of the cells of the 

 stigma, killing them, and thus rendering them incapable of absorbing 

 water. 



Toxic actions of this kind would appear to be the key to the explana- 

 tion of many of the most curious phenomena bearing on pollination. 

 It is well known, for example, that in certain Orchids, Oncidium flexuo- 

 sum, and others, to put the plant's own pollen on the stigmatic sur- 

 face is to poison it. The flower withers prematurely and fails to set 

 seed (see Darw^in's Annuals and Plants under Domestication, vol ii., 

 p. 115). 



It is just possible, as suggested by Fitting, that sterility may not 

 infrequently be due to a similar cause, and that it might be worth the 

 while of anyone who wished to obtain seed of a sterile form of Orchid, 

 or other plant, to immerse the pollinia, or pollen, in water or a weak 

 sugar solution for three or four hours, in order to remove the toxic 

 substance before using the pollen for breeding purposes. Again, it 

 appears probable that such a toxic action may be reciprocal ; that is, 

 that the stigma may, upon occasion, exercise a poisonous influence on, 

 and so prevent the developmerit of, the pollen. Here, again, artifice 

 may perhaps be used to overcome the difficulty. If the stigmatic 

 surface were wiped clean of its sticky fluid, and if, in place of that 

 fluid, other from the stigma of the pollen parent were smeared on the 

 stigmatic surface, it is possible that subsequent pollination might result 

 in fertilization. Only experiment can show whether either of these 

 suggested methods would prove of use, and such experiments are for 

 the botanist rather than the grower to carry out. 



No plants show better than the Orchids the diverse effects of pol- 

 lination, and, inasmuch as these effects have been analysed carefully by 

 Fitting, they must be described, albeit briefly. 



The chief changes induced by pollination of Orchids are : premature 

 withering of the flower ; swelling of the tissues of the column so as to 



