DEVELOPMENT OF PLANTS 349 



simple types of flowers are often developed in large numbers 

 upon an elongated stem (Fig. 262, A, D-G) and are rather sug- 

 gestive of a strobilus although the individual flower is more 

 comparable with a strobilus as will be seen especially in those 

 types where the sporophylls are numerous and arranged spirally 

 upon the receptacle of the flower (Fig. 264). A group or 

 cluster of flowers is called an inflorescence in contradistinction 

 to the solitary flower developed at the end of a branch or stem. 

 It is noticeable in these primitive angiosperms that the micro- 

 and mega-sporophylls are usually borne in separate flowers or 

 inflorescences ; compare Pinales, which are developed on separate 

 plants as in the willow or on different parts of the same plant as 

 in the cat-tail. This arrangement is probably associated with 

 the fact that the advantages of crossing or the transfer of the 

 microspores of one flower to the megasporophylls of another 

 is effected by the wind. In higher types, which include the 

 great majority of angiosperms, the micro- and mega-sporophylls 

 are developed in the same flower which is therefore said to be 

 perfect since it contains both of the organs essential for seed 

 production (Fig. 261^, 1). A type like the willow is termed 

 imperfect because the flower lacks one kind of sporophyll. 

 Crossing is effected in the perfect type of flower by the earlier 

 ripening of the micro- or mega-sporophylls and often also, by 

 the arrangement of the organs of the flower which is of such 

 a nature that the microspores cannot readily reach the mega- 

 sporophylls of the same flower. Insects are usually the agents 

 for the transport of the microspores in such cases. Flowers in 

 which the microspores mature and are shed from the anthers 

 before the stigma of the megasporophylls are ready to receive 

 them, are called protandrous, meaning that the microspores which 

 develop the male gametes, are the first to mature. If the mega- 

 sporophylls become receptive before the anthers open, the flower 

 is said to be protogynous, meaning that the pistil matures first. 

 It must also be borne in mind, although the devices for effecting 

 a crossing are almost universal among the various groups of 

 angiosperms, that there are equally elaborate provisions for the 

 transference of the microspores of perfect flowers to the stigmas 



