132 



PLANT STKUCTUKES 



Under certain other conditions prothallia are observed to 

 sprout directly from the leafy sporophyte instead of from 

 a spore. This is called apospoi'y, meaning " without a 

 spore." 



78. The gametophyte. — The prothallium, like a simple 

 liverwort, is a dorsiventral body, and puts out numerous 



Fig. 112. Stas-horn fern {Platycerium grande), an epiphytic tropical form, showing 

 the two forms of leaves : a and b, young sterile leaves ; c, leaves bearing spo- 

 rangia ; d, an old sterile leaf.— Caldwell. 



rhizoids from its ventral surface (Fig. 111). It is so thin 

 that all the cells contain chlorophyll, and it is usually short- 

 lived. In rare cases it becomes quite large and permanent, 



