FERTILISATION IN GYMNOSPEEMS. 291 



discharged. The plant is dichogamous and requires the pollen of 

 another flower to fertilise the pistil. In rare instances, 

 as in the Searpink (Armeria ma/ritima), the conduct- 

 ing tissue of the style at its lower part becomes 

 elongated so as to pass into the ovary, and ultimately 

 comes in contact with the ovide, when impregnation 

 takes place (fig. 517). 



The length of time during which the pollen re- 

 tains its vitality, or power of effecting fertilisation, 

 varies in different plants. According to Gsertner and 

 others, the pollen of some species of Mcotiana retains 

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

 species of Datura, two days ; pollen of Dianthus ^'s- 6i7. 



CaryophyUus,' three days; pollen of Lobelia splendens, eight or nine 

 days; poUen of Oheiranthus Cheiri, fourteen days; pollen of Orchis 

 abortiva, two months ; pollen of OandoUea, one year ; pollen of Date 

 Palm, one year or more. Michaux says that in some Palms, as Date 

 and Ohamserops humilis, the pollen may be applied successfully after 

 having been carefully kept for eighteen years. The pollen retains 

 its vitality longer when not removed from the anthers ; and the finer 

 it is, the more quickly it loses its fecundating property. 



In most flowering plants the pollen is applied directly to the 

 stigma, but in some cases when the plants are Gymnospermous, that 

 is, have no proper ovarian covering, and no stigma, the pollen is 

 applied directly to the ovule. The pollen then undergoes changes 

 by the formation of tubes, through which the fovUla passes in order 

 to come in contact with the minute cells in the ovule. The matter 

 called fovilla covered by the intine consists of minute molecules, 

 which often exhibit movements, to which the term molecular has 

 been applied. 



Embryogenic process in Gymnospermous Flowering Plants. 



In Gymnospermous plants, such as Coniferse (Firs and Pines, fig. 

 518) and Oycadaceae (fig. 519), impregnation is eflfected by direct 

 contact between the pollen and the ovule. There is no true 

 ovary bearing a stigma. Such is the view taken by many 

 botanists. There are however others of equally high authority 

 who do not adopt this opinion, and who look upon the so-called outer 

 covering as not solely composed' of the spermoderm, but as formed 

 partly of it and partly of the ovarian coat. Some speak of the 

 ovuliferous leaves in Oycads as being open carpels, and they also look 



, Fig. 517. Ovary, ov, of Sea^pmk (Armeria maritima}, in which the orule is suspended 

 hy a curved cord, cor, and the' conducting tissue, s, of the style elongates in a downward 

 direction. 



