Metaphyta Pteris. 



129 



tissue of the thallus. It thus approaches more closely to 

 the ovarium of a unisexual Fucus. The neck consists of four 

 vertical rows of cells each from four to six in number. The 

 enclosed canal contains two or more canal cells, while the 

 venter contains the large naked ovum. As in the moss, the 

 canal cells, before maturation of the ovum, become mucila- 

 ginous, and act in the first place as a wedge to force open 

 the canal mouth, and secondly, when expelled, as a trap to 



FIG. <-$.Ad ; antuin capillus- 

 venerls. THALLUS AND 



YOUNG FERN. (Sachs.) 



FIG. 57. Pteris scrrulata. 

 OVARIUM. (Sachs.) 



b, first leaf ; w'. w", roots ; 

 h, root-hairs of thallus,/,/. 



catch the sperms and conduct them to the mouth of the 

 ovarium. One or more sperms touch and fuse with the 

 ovum, thus fertilising it. The fertilised ovum, or embryo, 

 soon begins to segment into a number of cells, which early 

 in their history show indications of the respective parts of 

 the mature plant to which they are to give rise. That por- 

 tion of the embryo next the bottom of the venter becomes 

 the apex of the young stem, and a peculiar organ known as 

 the foot ; the part of the embryo pointing towards the neck 

 becomes the root and first leaf. The foot acts as an organ 

 for the transference of the nourishment from the nurse-like 



K 



