xv THE DEVELOPMENT OF THE FLOWER 201 



marking the line of junction between two pollen sacs, when the 

 opening is called longitudinal dehiscence. In other cases the 

 anther opens by small pores, as in the Heath and Potato, when 

 the dehiscence is porous. In the Barberry, the anthers open by 

 small doors or valves when the dehiscence is valvular. 



The Structure of the Gyncscium. The gyncecium con- 

 sists of modified foliage leaves which depart even more widely 

 than the stamens from the ordinary foliage leaf type. The 

 structure of the carpels, as these modified leaves are called, can 

 be made out if transverse sections are cut and examined by the 

 microscope. Each carpel is found to consist of the following 

 parts : 



I. Lower and upper epidermis. 



2. Several layers of mesophyll. 



3. A number of vascular strands which penetrate the 

 mesophyll, and bring nutritive material to the carpel and its 

 ovules. 



The gyncecium may consist of a single carpel, as in the Pea ; 

 or of several carpels, as in the Poppy and Lily. In every case 

 the carpel or carpels are united so as to form a cavity or cavities 

 the ovary. In the ovary the ovules are developed, and they 

 receive the materials necessary for their further growth from the 

 ovary. 



The Structure of an Ovule. An ovule consists of the 

 following parts : 



i. The funiculus or stalk by which it is attached to the 

 placenta or swelling on the wall of the ovary (p. 10). 



2. The integuments or coverings of the ovule, which are 

 several layers of cells in thickness. There is a small opening 

 through the integuments, the micropyle. (p. 10). 



3. The nucelluS) an oval mass of tissue within the integu- 

 ments. 



4. The embryo-sac embedded in the nucellus. 



The Embryo-Sac. The embryo-sac is a large oval cell 

 which contains : (i) The embryo-sac nucleus placed in the 

 centre of the sac. (ii) The egg-apparatus, which consists of 

 three cells at the micropyle end of the embryo-sac. One of 

 these receives the name of the ovum or oosphere and is the cell 

 from which the embryo is developed. The other two form the 

 Synergidce, and direct the pollen tube to the oosphere. (iii) The 



