164 STRUCTURE AND LIFE HISTORIES 



(Cystopteris bulbifera) received its specific name from the 

 fact that it bears bulbils. A third method is illustrated 

 in the very interesting "walking fern" (Camptosorus 

 rhizophyllus) , where the tips of the long acuminate leaves 

 rest upon the moist ground, take root, and develop an 

 entire new plant at the distance of the leaf's length from 

 the parent fern (Fig. 122). The result of several repeti- 

 tions of this suggested the common name " walking fern." 

 A fourth method is by means of stolons or "runners" 

 (Fig. 123). 



150. Dispersal of Spores. After the spores are mature 

 the essential need is that they become dispersed, so that 



FIG. 124. Tips of two sporophylls of the fern, Drynaria meyeniana, 

 showing the large marginal sori. The black dots adjacent to the leaf-tips 

 are spores projected onto white paper by the snapping of the sporangia. 

 The specimens were covered with a bell-jar. 



they may find favorable conditions of moisture, tem- 

 perature, light, and soil for development; for, with rare 

 exceptions, such conditions do not obtain within the 

 spore-case. Moreover, if the spores remained within the 

 sporangia they would be so greatly crowded that only a 



