ii + 



ANGIOSPERMAE. 



The alternation of sexual and asexual generations, such 

 a dominant feature in the life-cycle of the Archegoniatae, 



is here quite obliterated, the sexual organs being produced 

 by the sporophyte. 



The male organs, called pollen grains, develop in 

 anthers, and these are mostly borne at the end of slender 

 stalks ealled filaments, filament and anther forming the 

 stamen. 



The female organ, the embryo-sae, is embedded in 

 an ovule, which in its turn is situated within the pistil. 

 An ovule generally consists of three parts, viz. one or two 

 integuments, the nucellus and, embedded in the latter, the 

 embryo-sac. It possesses an opening or a channel called 

 the micropyle. The pistil is generally produced at its 

 apex into a style, and this bears a receptive surface at its 

 end, termed the stigma. 



The pollen grain is transported to the stigma mostly 

 by outside agency, viz. by wind, insects or birds and in a few 

 cases, where the flowers are submerged, e.g. Ceratophy/luni, 

 Zoste?Yi, Najas, by currents in the water", but occasionally 

 there is also self-pollination by direct contact between 

 anther and stigma, e.g. Viola, Anacampseros, Argyrolobinm. 

 The pollen grain germinates on the stigma, emitting a 

 slender thread called the pollen tube. This tube carries the 

 sexual nucleus of the pollen grain in its apex and, penetrating 

 through the tissue of the style into the ovular cavity of the 

 pistil, enters the ovule, in most cases through the micropyle. 

 In this way the sexual nucleus of the pollen grain reaches 



* If" the pollen of plants is transported from flower to flower by wind, tlie\ are 

 termed "anemophilotts" ; it by insects "entomophilous" ; if by birds fl omithophilou8 ,, i 



and if by water li hyd/rophUoU8." 



