362 



FOURTH GROUP. SEED-PLANTS. 



(Fig. 286 A), from which a vascular bundle is usually formed, passing through the 

 middle of the connective, while the outermost peripheral layer forms the derma- 

 togen or young epidermis. According to Warming's minute investigations it is. 

 only the layer of tissue immediately under the epidermis, the outermost layer of 

 periblem, which gives rise both to the archesporium and to the parietal layers which 

 surround the archesporium in each pollen-sac. In other words this layer next 

 beneath the epidermis in each of the four longitudinal protuberances separates into 



FIG. 289. Funkia ovata. Formation of pollen, (see 

 the text). In VII the wall of one daughter-cell has burst 

 owing to the absorption of water, and the protoplasm is 

 escaping through the fissure and remains lying in front of 

 it rounded off into a spherical form. The details of the 

 cell-division are not shown in the figure, which was drawn 

 a long time ago- Magn. 550 times, 



FIG. 288. Funkia cordata. A transverse section through a 

 young pollen-sac before the isolation of the mother-cells sm ; ep 

 the tapetal cells, -w the wall of the pollen-sac. B the loculament of 

 the pollen-sac after the isolation of the mother-cells sm ; ep indica- 

 tion of the tapetal cells. For the further development of the 

 pollen-mother-cells and of the pollen see Figs. 289 and 290. Magn. 

 500 times. 



FIG. 290. B a young pollen-cell of 

 Funkia ovata ; the bead-like thickenings 

 which project outwardly are still small, 

 but larger in the older cell C; they are 

 disposed in lines connected into a net- 

 work. 



two layers, the innermost of which is the archesporium. The cells of the arche- 

 sporium very soon become distinguished by their size as compared with those of the 

 surrounding tissue, and when seen in a transverse section of the anther they usually 



