Z-1U FERTILIZATION OR FECUNDATION. 



food, detach the pollen masses, which are easily removed from the 

 clinandrium, or the part of the column on which they are placed, and 

 then naturally fall on the stigmatic surface. Bees and aphides may, 

 in many instances, contribute to the process of fertilization. 



499. While the pollen is being elaborated, the stigma is also under- 

 going changes. It secretes a viscid matter ready to detain the pollen- 

 grains when they are discharged. This secretion was represented by 

 Dr. Aldridge to be, in some cases, acid ; but it seems more generally 

 to be of a mucilaginous or saccharine nature. Vaucher thinks that 

 the nectariferous fluid usually found in the flower spreads itself over 

 the stigma, and that it is sometimes instrumental in conveying the 

 pollen-grains. In Goldfussia or Ruellia anisophylla, and the species 

 of Campanula, as media, Eapunculoides, and Trachelium, the style is 

 covered with collecting hairs, which appear to aid in the application 

 of the pollen. In the first-mentioned plant, a remarkable curvation of 

 the style takes place, so as to make the stigma come into contact with 

 the hairs. In Campanula, the hairs on the upper part of the style 

 seem to collect the pollen, and allow it to be applied to the revolute 

 branches of the stigma. In this genus the style is at first slightly 

 longer than the stamens, but it soon becomes twice their length, and 

 during its elongation, the hairs xipon it brush the pollen-grains out of 

 the anther cases, and thus raise them into a position where they can 

 be applied ultimately to the stigmatic surface. The stigma consists of 

 two branches, which are at first erect, but afterwards, by changes in 

 the cells, become completely revolute, so as to come into contact with 

 the hairs. After the hairs have performed their office, their fine inner 

 membrane collapses by a process of endosmose, and the stiff outer 

 membrane is drawn inwards, so as to retire within its cell. After the 

 pollen reaches the stigma, changes take place in it, by which the fovilla 

 contained in the intine of the grains is allowed to escape. This fovilla 

 consists of minute molecules exhibiting certain movements, which by 

 some have been considered analogous to those of phytozoa in Crypto- 

 gamic plants, or spermatozoa in the animal kingdom. Others look 

 upon these motions as entirely molecular. 



500. The length of time during which the pollen retains its vitality, 

 or power of effecting fertilization, varies in different plants. Accord- 

 ing to Gzertner and others, the pollen of some species of Nicotiana 

 retains its vitality only for forty-eight hours ; pollen of various species 

 of Datura, two days ; pollen of Dianthus Caryophyllus, three days ; 

 pollen of Lobelia splendens, eight or nine days ; pollen of Cheiranthus 

 Cheiri, fourteen days ; pollen of Orchis abortiva, two months ; pollen of 

 Candollea, one year; pollen of Date Palm, one year or more. Michaux 

 says, that in some Palms, as Date and Chamaarops humilis, the pollen 

 may be applied successfully after having been carefully kept for 

 eighteen years. The pollen retains its vitality longer when not removed 



