5o6 



PHANEROGAMS. 



one. This smaller cell now again undergoes a transverse division parallel to the 

 first, and this is sometimes followed by a second ; a two- or three-celled body is 

 thus formed, attached on one side to the intine, and projecting into the cavity 

 of the larger cell, as in Abietineae, which, moreover, further resembles Ceratozamia 

 in the fact that, as in the Coniferae, the large cell, formed by the first division of the 

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

 inactive in the pollen-grain. In Cycas Rumphu, 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 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. 344). The ovule is always orthotro- 

 pous, and consists of a large nucellus and a thick integu- 

 ment 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 nucellus. According to De Bary's 

 researches a second inner integument appears to exist in 

 the case of Cycas revoluta. [In the nucellus a group of 

 cells can be readily distinguished at an early stage, which 

 Warming considers to be homologous with the mother- 

 cells of the spores in the sporangia of the Vascular Crypto- 

 gams; from one of these the embryo-sac is formed. The wall of the embryo- 

 sac becomes thickened, and its cavity becomes filled with endosperm. From 

 certain superficial cells of the endosperm the archegonia (corpuscula) are formed. 

 The neck of the archegonium consists of two cells. From the large central cell 

 a canal-cell is cut off, leaving the remainder as the oosphere. After fertilisation, 

 each oospore gives rise to a single suspensor ; the embryo is not developed 

 at its apex until after the seed has been sown. The embryo of Ceratozamia has 

 only one cotyledon ; Cycas and Macrozamia have two ; Van Tieghem has, however, 

 found two cotyledons in some cases in Ceratozamia Mexicana, and three in Zamia 

 spiralis^ 



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 polli- 



Fl<;. 345- — CeriuostuHta iongi- 

 folia (after Juranyi) ; A pollen- 

 grain containing a group of three 

 (vegetative) cells y; B develop- 

 ment of the pollen-tube from the 

 large cell of the grain ; e the ex- 

 tine, bs the pollen-tube covered 

 by the intine. 



