MORPHOLOGY OP LEAVES AND FLOWERS 619 



Fig. 481. Cross section of the ovary of Gesneria showing one cell and two 



parietal placentae. 

 (After Thome.) 



five loculi. This indicates that the pistil of oxalis consists of five 

 carpels whose ovaries have united to form one with five loculi. 

 This uniting may even extend to the styles and stigmas. A pistil 

 that is made up of more than one carpel is compound. 



Fig. 482. I. Cross section of the compound pistil of Snapdragon, showing the 

 two cells and the axillary placentae. II. Longitudinal section of an ovary 

 with a free central placenta. 



(After Thome.) 



Ovule. — The ovule is the most essential part of the pistil because 

 it is the forerunner of the seed. The ovule consists of a central 

 portion, the nucellus, which is enclosed by one or two jackets which 

 are called the integuments. The integuments do not entirely close 

 at the outer end of the nucellus and this small opening left is the 

 micrppyle through which the pollen tube usually passes. In the 

 interior of the nucellus is a region which resembles a large cavity 

 since it contains no cell walls. This is the embryo sac. At about 

 the time the flower opens the embryo sac contains seven cells. The 

 two which have an important future history are the egg and en- 

 dosperm cells. 



