CHAPTEE XII 



FRUITS AND SEEDS 



§ 44. How are fruits and seeds formed ? 



In discussing the structure of a complete flower, we mentioned 

 that the centre of each flower was occupied by the pistil, 

 which consists of an ovary, a style, and a stigma. Of these 

 three parts the stigma is the apparatus for catching and 

 retaining the pollen, the style the channel along which the 

 pollen tube grows when the pollen grain germinates, and 

 the ovary is the receptacle where the ovules are produced and 

 develop into the seeds. The pistil is either formed of a 

 single carpellary leaf, the margins of which have been folded 

 in and have become fused, or several leaves arranged in a ring 

 have become fused together, in which case usually the ovary 

 will consist of several chambers. As already mentioned, the 

 tube-like elongation between the ovary and the stigma, the 

 style, is relatively of little importance, and is not developed in 

 some plants, the stigma being situated directly on the ovary. 

 Such is the case in the pistil of the grass represented in 

 Fig, 31. Here the stigma is feathery and very delicately 

 developed; its numerous filamentous branches rendering it 

 very ef&cient in capturing the pollen grains, which are easily 

 carried about by the wind. The main branches (ff) which bear 

 the feathery processes are directly continuous with the tissues 

 of the ovary (/), which presents only a single cavity, the 

 latter being completely filled by the single ovule (0). This 

 consists of a very delicate tissue, which is differentiated into a 

 central portion and an enveloping layer. This latter is formed 

 by two integuments (i), which do not completely close in the 

 central nucellus, but leave a very small passage open to the 

 latter. This opening is termed the miCFopyle. 



