28 EVOLUTION OF PLANTS 
While in the lower groups the sexual cells are borne 
in cells differing but little from the vegetative ones, 
the higher algz, mosses, and ferns have them con- 
tained in multicellular structures of very characteristic 
form which may properly be considered as true sexual 
organs. 
A marked degeneration of the sexual cells is observed 
in many fungi where, when present at all, they are 
usually reduced in structure and sometimes apparently 
functionless, while in very many of them no traces of 
sexual organs have as yet been discovered. 
Among the flowering plants there are produced. spe- 
cial accessory structures connected with reproduction 
but not to be considered strictly themselves as repro- 
ductive. ‘The various parts of the flower are of this 
nature, the true reproductive organs being special 
minute structures within the pollen-grain and ovule. 
The development of brightly colored and sweet-scented 
flowers is doubtless connected with the fertilization of 
the germ-cells within the ovule, and the same is true of 
the various mechanical devices for insuring pollination 
through insect agency. The correlation of structures 
in flowers and insects is often extraordinary, and is 
sometimes so great that a single species of flower and 
insect are absolutely dependent on each other for their 
existence. We shall, however, consider this question 
more at length in a later chapter. 
A high degree of specialization is also seen in the 
subsidiary reproductive parts of plants other than the 
seed plants, although less marked than in those. Thus 
in the mosses and ferns there are very perfect me- 
chanical devices for distributing the ripe spores. The 
