366 PRIMITIVE FLOWERS 



should be noted In the cat-tail that numerous spirally arranged 

 hairs are associated with the sporophylls. These are supposed 

 to represent sterile sporophylls and this is borne out by the fact 

 that primitive flowers are characterized by just such an arrange- 

 ment of their sporophylls, and also by the fact that in an allied 

 genus spirally arranged sporophylls actually occur. These simple 

 types of flowers are often developed in large numbers upon an 

 elongated stem (Fig. 262, A, D-G) and are rather suggestive 

 of a strobilus although the individual flower is more comparable 

 to 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 soli- 

 tary 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 in- 

 florescences (compare Finales) 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 A, i). 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 stigmas 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- 



