CVCADE.E. ._,j 



pollen-grain, developes into the pollen-tube, the mass of small cells remainino- 

 inactive in the pollen-grain. In Cjras Riimphii, Encephalartos, and Zamia, the 

 pollen-grain also splits up, according to De Bary, into a larger and a smaller cell, 

 the latter also in this case again dividing once, and the larger cell developing into the 

 pollen-tube. The spot where the intine which developes into the pollen-tube breaks 

 through the extine, lies exactly opposite the mass of small cells (the secondary 

 cells of the pollen-grain) ; the extine is in this place thinner, and in the dry 

 pollen-grain deeply folded in, so that the transverse section of the dry pollen-grain 

 is kidney-shaped. During the absorption of water however which precedes the 

 formation of the pollen-tube, the pollen-grain again assumes a spherical form. 



The carpellary leaves are arranged spirally or in apparent verticils, closely 

 crowded on the axis of the female flower. Those of Cycas have already been 

 described; in Zamia, Encephalartos, Macrozamia, and Ceratozamia, the carpels 

 are much smaller, and each bears only two ovules, attached right and left to a 

 peltate expansion which terminates a slender pedicel (Fig. 315). The ovule is 

 always orthotropous, and consists of a large nucleus and a thick integument the 

 inner layer of which (in contrast to that of other Phanerogams) is penetrated by 

 a number of fibro-vascular bundles. The micropyle is a slender tube, formed by 

 the prolongation of the contracted margin of the integument beyond the summit 

 of the nucleus. According to De Bary's recent researches a second inner inte- 

 gument appears to exist in the case of Cycas revoluta. But little is known about 

 the formation of the embryo-sac, or of the endosperm, which is strongly developed 

 long before fertilisation, or of the large central cells, easily visible to the naked eye 

 (in Cycas from 3 to 4 mm. long), or finally of the long suspensors. The main 

 point is that in all these respects Cycadeae agree essentially with Coniferae. The 

 central cells are formed in large numbers in the same endosperm, but not until the 

 ovule has already attained a considerable size. The suspensors, each of which 

 gives rise to several rudimentary embryos, but only one of which developes into 

 a perfect embryo, may still be detected in the ripe seed as a ball of long threads, 

 the central cells themselves being also discernible even in the ripe seed. 



In consequence of the form and position of the carpels, the ovules are covered and 

 concealed before and after fertilisation, except in Cycas ; at the period of pollination, 

 which is apparently brought about by insects, the carpels separate from one another, 

 and the micropyle excretes a fluid to which the pollen-grains adhere. The outer 

 layer of the testa is usually fleshy, the inner one hard, and the seed therefore 

 resembles a plum, with its surface often brightly coloured. 



