ORCHID CONFERENCE. 



407 



Zygopetalum Mackayi, it will, I think, be of interest if I bring this 

 I paper to -a close by describing the progress of attempts to unravel the 

 ' several processes which are set going in the floral mechanism as a 



consequence o'f pollination. 



All gardeners know that pollination does indeed set going a long 



series oi changes in the flower and even in the neighbouring parts of 



the plant. 



It is a well-known fact, for example, that many pollinated flowers 

 wither more rapidly than unpollinated flowers. 



So' marked, indeed, is the difference between pollinated and un- 

 pollinated flowers in this respect, that it is worth while in the case of 

 certain self-fertilized flowers to prevent pollination by the removal of 

 the pistil or stamens. 



Again, it is a notorious fact that some seedless fruits, certain 

 grapes, currants, &c., do not swell unless they are pollinated. Pollina- 

 tion is useless so far as inducing seed-formation is concerned, but it 

 nevertheless fulfils the secondary purpose, in some seedless fruits, of 

 giving rise to a chemical stimulus under which the fruit walls swell 

 and become fleshy or succulent. 



These illustrations, which might, of course, be multiplied, serve to 

 demonstrate that pollination, besides bringing about fertilization, sets 

 up disturbances in the flower, and even in other parts of the plant. 



The nature of these disturbances has been investigated recently m 

 orchids and other plants, and as a result of these investigations, 

 although they leave much unexplained, we know definitely that pollina- 

 tion may bring about three types of events. First, fertilization, of 

 which we have treated already. Second, changes due to the contact 

 of pollen with the stigmatic surface. Third, results which may be 

 described as intoxications, or responses to chemical stimulation. Illus- 

 trations of marked results arising as the consequence of mere contact 

 of the pollen with the stigmatic surface are exhibited by plants such as 

 Mimulus, by orchids, and, doubtless, by many others. 



Place a little of its own pollen on the stigma lobes of Mimulus 

 cardinalis , and they begin to close. If more pollen be placed on the 

 i lobes they close sooner, and remain closed longer. If much pollen 

 be used in the experiment the lobes remain closed; if only a little be 

 I placed on the stigma, the lobes separate after a short time. 

 I Careful experiments by Lutz have shown that the closing move- 

 ment is due to a contact stimulus. As has been known for a long time, 

 ; ilie closing movement of the .stigma lobes of Mimulus and similar plants 

 I with sensitive stigmas may be brought about by stroking the surface 

 I of the stigma with the finger-nail or with a knife. 

 I The cells of the stigmatic surface are in tension, and charged with 

 1 water. The irritation, either by a load of pollen or by stroking or 

 j scratching, brings about a discharge of water from these cells. Tliose 

 I of the upper surface lose more, and contract more, and, shortening, pull 

 t the lower surfaces upwards till the lobes meet. 



Any pollen, alive or dead, will serve to bring about this closure, hut 



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