ORCHID CONFERENCE. 



409 



enclose the stigmatic surface ; swelling and greening of the ovary ; and 

 development of the ovules. Fitting worked with species such as 

 Phalaenopsis violacea and P. amahilis, the unpollinated flowers of 

 which, in their native habitat, persist for a month or more. He showed 

 that withering, as I have indicated already, is the result of contact 

 stimulus. It is induced when not only living, but also dead pollen, or 

 even grains of sand, are placed on the stigmatic surface. Although the 

 withering effect is due also to a contact or wound-stimulus applied to 

 the stigmatic surface, the second consequence of pollination, the arching 

 of the column over the stigmatic surface (fig. 142), is not. This effect 

 is not induced by sand or other fine particles, although it is produced 

 by the. plant's own pollen which has been killed by exposure to steam 

 or chloroform. It is the result of a chemical stimulus or intoxication, 

 as is proved by the fact that a watery extract of the plant's pollen, if 

 put on the stigma, induces the swelling (fig. 142, d). 



Thus a little cotton wool which has been dipped in such an extract 

 suffices, when placed on the stigma, not only to produce withering by 

 its contact effect, but also to produce the swelling of the column by its 

 chemical effect. 



ABC D 

 Fig. 142. — Phalaenopsis amabilis. 



(A) column stigma unpollinated ; (B) column six days after pollination of 

 stigma J (C) column six days after polHnation " with dead pollen; (D) section 

 of column after " pollination " with cotton wool soaked with pollen extract. 

 (Fitting.) 



Further, the swelling and greening of the ovary only occur after 

 the pollen tubes have grown some way down towards the ovary, and 

 these changes are to be attributed to yet another chemical effect pro- 

 duced by substances excreted by the developing pollen tubes. 



Such, in brief, are the facts which recent research has brought to 

 light with respect to the significance of fertilization, and the origin of 

 the accessory effects of pollination. They show in graphic way what a 

 highly organized mechanism is the flower. They indicate that it is 

 attuned to respond in definite manner to different kinds of stimulation, 

 and they prove that many responses on the part of the plant are called 

 forth by definite chemical substances. Although our knowledge is yet 

 too imperfect for it to be of evident service to the Orchid raiser, it is 

 not without promise that it may throw light on the strange phenomena 

 of sterility, and perhaps provide us with means of overcoming that 

 refractoriness. Thus we may anticipate the making of yet more 

 wonderful mongrels than those which now delight the amateur, con- 

 found the botanist, and confuse the student of nomenclature. 



