CHAPTER XIII 

 REPRODUCTION 



IN previous chapters we have dealt with the structural pro- 

 visions for those functions that have to do with the nutrition 

 and maintenance of the individual. We shall now find that 

 the organization of the individual is not related to its own needs 

 alone, but that it provides also for the continuance and pro- 

 gressive evolution of its race. This is accomplished by the 

 sporogenous cells and tissues occurring in the ovules and anthers 

 of the spermatophytes and in their homologues among the 

 lower forms, by spores themselves, by gametes (sperm cells 

 and egg cells), and by nurse cells having for their chief or only 

 function the nutrition of the new generation, such as tapetal 

 cells in sporangia, and antipodal cells within the embryo sac. 

 These tissues are often meristematic it is true, but their purpose 

 is so different from that of the vegetative meristems (see page 24) 

 that they cannot be classed together. Those tissues which 

 have reproduction for their chief or only function should be 

 classed as Reproductive Tissues. For our introduction to 

 tissues of this sort we cannot do better than to trace the develop- 

 ment of a fern sporangium. 



Development of Fern Sporangium. Figure 122 has been 

 made from camera lucida drawings of a longitudinal section 

 through the apex of a sporophyll of Aneimia phyllitidis. At 

 a is the primordial meristem of the growing apex, and at b, c, 

 d, e, /, are successive stages in the formation of sporangia pro- 

 ceeding from this meristem. It appears that a sporangium has 

 its beginning in a group of primordial cells such as is seen at i. 

 These evidently divide parallel to the surface (periclinal division) 

 and again perpendicular to the surface (anticlinal division), 

 and the growth of the daughter-cells causes the enlargement 

 which we recognize as the beginning of the sporangium, b. At 



213 



