FERTILIZATION IN 6YMN0SPEEMS. 419 



seed. A characteristic feature, occurring shortly before fertilization, is the cutting- 

 oiF of a small cell from the summit of the egg-cell. This little bi-convex cell (shown 

 at the tip of the right-hand egg in fig. 315 2) is known as the "ventral canal-cell". 

 A similar cell is cut off in the Ferns, &c., and lies at the base of the neck of the 

 archegonium just above the egg-cell. It is afterwards absorbed. 



From a comparison of the structures in the ovule of a Gymnosperm with those 

 arising on the Fern-prothallium, or Moss-plant, it seems probable that the egg-cell, 

 with its neck in the former, corresponds to the archegonium of the latter, though 

 the archegonium in the Gymnosperm is somewhat reduced when compared with the 

 exposed archegonium of Ferns and Mosses. 



The number of egg-cells ( = archegonia) produced in the ovule of a Gymnosperm 

 is various. In the Spruce Fir and Pine there are from 3 to 5, in the Cypress and 

 Juniper 5 to 15. In the Firs and Pines the egg-cells are well isolated from one 

 another by layers of endosperm, in which they are embedded; in Cypresses and 

 Junipers the egg-cells are all in immediate contact, forming a rosette-like cluster 

 at the top of the endosperm under the micropyle. The tissue in which they lie 

 embedded, the endosperm, is in Gymnosperms pretty extensive, and being well- 

 stocked with food-materials, forms, after fertilization, a nutritive bed for the young 

 developing embryos, and is ultimately absorbed by them. 



In the Angiosperms, on the other hand, the ovules are not exposed on open 

 scales, as in Gymnosperms, but inclosed in definite chambers, the ovaries. Pollen is 

 brought to the stigma (not to the micropyle, as in Gymnosperms), and fertilization 

 is accomplished by the development of pollen-tubes, which penetrate the tissues of 

 the style to the ovules. In Gymnosperms there are no ovaries or styles or stigmas. 

 Pollen is brought by the wind direct to the micropyle of the ovules. Various 

 arrangements exist for bringing the pollen-grains into the micropyle and for hold- 

 ing them there. Just at the time when pollen is liberated from the male flowers 

 the micropyle is opened wide, and its lining cells are rendered sticky by a mucila- 

 ginous secretion, so that the pollen brought by the wind sticks to it. This mucilage 

 often projects as a little droplet from the micropyle, and in it the pollen-grains are 

 caught; as this drop gradually dries up and contracts the pollen-grains are sucked 

 into the micropyle, so that the grains come to lie right on the tip of the nuceUus of 

 the ovule, from which point they germinate, putting out their tubes (cf. fig. 315 ^). 

 These drops of mucilage can be well seen in early spring on the exposed ovules of 

 the Yew-tree {Taxus haccata). This plant is dioecious, and on the female plants the 

 tips of the ovules project from a few scale-like wrappings, which envelop the base 

 of each ovule {cf. figs. 336^ and 336^). At the time when the male flowers are 

 intrusting their pollen-grains to the wind (usually in March) one may see the 

 female plants, on a sunny morning sparkling in the sunshine as it were with dew- 

 drops. These "dew-drops" are in reality droplets of mucilage, excreted from the 

 micropyles of the ovules, awaiting the chance deposition by the wind of pollen- 

 grains. By and by they dry up and the entangled grains are sucked into the 

 micropyle. In Gymnosperms it is the micropyle, not the stigma, which is pollinated. 



