CHAPTER XIII. 



THE OVULE. 



Origination from a Placenta on the carpel Nucellus, Integuments 

 and Micropyle Chalaza Embryo-sac Coats Sizes and 

 numbers Erect, Suspended, Horizontal, Pendulous and As- 

 cending ovules Orthotropous, Campylotropous and Anatropous 

 ovules Hilum, Chalaza and Raphe Positions as regards axis 

 Marginal, Parietal, Superficial, Axile and Free-central Placenta 

 Development of ovule Sporogenous cells, &c. Mother-cell 

 of Embryo-sac Development of Egg-apparatus Embryo-sac 

 nucleus Oosphere Antipodal cells Endosperm Corpus - 

 culum of Gymnosperm Archegonium Homologies. 



THE rounded structures found in the ovary or on the 

 carpels, and which are to become the seeds, are called 

 Ovules, and in most cases they arise from the carpellary 

 leaves, at the margins or other places where they are 

 attached (placenta). Before going into details we will 

 note some characters used in describing the ovule. 



In rare cases the ovary contains a single ovule, spring- 

 ing from its base and standing erect. A longitudinal 

 median section through such a typical ovule (e.g. Buck- 

 wheat, Pinellia, &c.) shows an ovoid or pyriform nucellus, 

 invested from below with one or two integuments, which 

 nearly close it in above at a point opposite the base of 

 attachment : the aperture left uncovered is the micropyle, 

 and is the minute passage into which the pollen-tube 

 penetrates eventually. 



