53 



may be provided with bristles, points, spur-or horn -like pro- 

 cesses. The connective is also sometimes prolonged ' into a 

 point beyond the anthers. The filament is usually slender, but 

 varies in shape and is sometimes provided with wings. 



Pollen is usually a powdery substance, which, when magni- 

 fied, is seen to consist of distinct grains. The shape and size of 

 the grains varies in different plants and the surface of the 

 grains may, or may not, be provided with points, knobs, 

 ridges, or other markings. In those plants, the pollen of which 

 is distributed by the wind, the grains are smooth and in others, 

 the pollen of which is distributed by insects, or birds, the 

 grains are usually sticky. In some plants the grains adhere 

 together in masses, the latter being called pollinia. 



50. As has been already pointed characters 



out, a simple pistil really consists of a single infolded of 

 leaf which bears the ovules on its inner margins. Such 

 an ovuliferous pistil-leaf is called a carpel. A pistil con- 

 sisting of one carpel is said to be simple, if of more than 

 one carpel it is compound. A gynoecium consisting of simple 

 pistils is called apocarpous, the carpels being distinct, a gyn- 

 cecium consisting of a compound pistil is syncarpous, the 

 carpels being combined. In a simple pistil the lower 

 surface, or back, of the carpel is represented by the exterior 

 of the pistil, the upper surface, or front, of the carpel forms 

 the interior of the pistil. The united margins of the carpel 

 which bear the ovules look towards the centre of the flower 

 (the axis) and form what is called the ventral suture or seam. 

 The opposite ridge, along the back of the pistil, representing 

 the midrib of the carpel, forms the dorsal suture. In a com- 

 pound pistil the carpels may be joined by their margins only, 

 or these may grow inwards and be united in the centre of 

 the pistil. In the former case the pistil is one -celled and in 

 the latter it is divided by partitions called dissepiments into 

 several cells, there being as a rule as many cells as there are 

 carpels. (Sometimes this is not the case, there being so-caQed 

 false-partitions which grow in from the back of the carpels.) 



The surface on which the ovules are borne, which is often 

 more or less enlarged, is called the placenta and the way in 

 which the placentae are arranged is called the placentation. In 

 the case of a compound pistil in which the carpels cohere by 

 their margins only, the placentae are on the walls of the pistil 

 and the placentation is called parietal ; when the margins are 

 brought together and cohere in the axis of the pistil, the 

 placentae are in the inner angles of the cells, and the placenta- 



