286 DEPOSITION OF POLLEN. 



as the stigma is withered they begin to wither also, or they become detached 

 from the flower and fall off. The withering of the petals occurs in very many 

 ways. They lose their turgidity, shrink up, occupy less space, and at the same 

 time change their colour. A change takes place in the petals of most flowers 

 which last only a day, a change similar to that which occurs in foliage - 

 leaves which have passed through a sharp night frost in autumn and then 

 been exposed next day to the sun — i.e. they exude water from their tissue and 

 become pulpy and look as if they had been squashed or boiled. The corollas 

 of some Papilionaceee, especially several species of the Clover genus (Trifolium), 

 dry up and rapidly become like withered leaves. The mean between these 

 two instances is furnished by those numerous plants whose flowers become limp, 

 shrink up somewhat, bend over, and then when withered fall ofi", as, for 

 example, in most Cruciferse, Valerians, and Compositse. The petals in withering 

 often assume the position which they occupied originally in the bud. Thus, for 

 example, the tongue-shaped flowers of the Goat's Beard (Tragopogon) roll together 

 into a tube on withering, and thus have the same appearance as just before 

 blossoming. Of course this is not always the case, for the tongue-flowers of 

 Bellidiastrwm and of most Asters roll spirally outwards when they fade, those 

 of Hieracium staticefolium spirally inwards, and it is not rare for fading, 

 drying, and discolouring petals to undergo corkscrew-like torsions. The con- 

 nection between the withering and the discoloration which accompanies it has 

 already been mentioned (p. 222). In many plants it happens that petals drop 

 from the flower either singly or all together after the deposition of pollen on 

 the stigma without having previously withered at all. Examples are furnished 

 by Eoses, Almonds, Primulas, and Fuchsias. 



It has been repeatedly shown by researches instituted for the solution of the 

 question that the sudden withering and falling of the petals is really dependent 

 on the deposition of pollen on the stigma, i.e. on the penetration of pollen-tubes 

 into the stigmatic tissue. If of two flowers which open simultaneously one is 

 provided with pollen and the other is shielded from it, or rather if the stigma 

 of one flower is purposely pollinated while the other is guarded from the 

 deposition of pollen, the latter will last longer and will not fall as soon as 

 the former. In two blossoms of a Flax (Linum grandifiorum), which opened 

 at the same time and were treated in this way, the corolla remained 35 hours 

 on the flower whose stigma was pollinated, but 80 hours on the other flower 

 whose stigma had received no pollen. Of two flowers of Anagallis Philippi 

 the corolla fell in four days from the one which had been pollinated, but 

 remained for six days on the flower whose stigma had been protected from 

 pollen. In a plant of Mammillaria glochidiata the flowers which were pollinated 

 appeared pulpy and permanently closed two days before those whose stigmas 

 remained free from pollen. Orchids as cultivated in hot-houses ofier a very 

 well-marked example of this same property. Normally these flowers are free 

 from insect-visits in the hot-house and their flowers remain fresh for many 



