EMBEYOGENY IN EQUISETACE^ AND EEENS. 281 



frond ; while in Mosses the spore forms the prothallus and the leafy 

 stem without impregnation, and this operation gives rise to the 

 formation of the stalked theca. 



The reproduction of Equisetacese (fig. 512), Horsetails, resembles 

 much that of ferns. Their spores, which are surrounded 

 by hygrometric filaments, caUed elaters, germinate 

 and form a lobed prothallus bearing antheridia at the 

 top of its lobes and archegonia at its base. The an-- 

 theridia appear as ovoid swellings containing at first 

 globules, which ultimately are developed as spermatozoi4s 

 (antherozoids).' The archegonia consist of globular 

 bodies, terminated by a long neCk with a four-lobed 

 opening at the top. The spermatozoids enter by the 

 opening and fertilise a cell in the archegonium, which 

 ultimately constitutes the germ of the new plant. 



Ferns, Ophioglossacese and Equisetacese, are called 

 isosporecB (/tfos, equal), because they produce a single 

 kind of spore, which in its turn gives origin to a pro- 

 thallus furnished with chlorophyll and roots, and capable 

 of independent existence. On the same prothallus, or 

 on two neighbouring ones, antheridia first of all origin- 

 ate, and when mature emit spermatozoids, then follow 

 archegonia generally formed of a central cell, to which 

 access is gained by a canal opening outwards. Fecun- 

 dation being effected by the entrance of spermatozoids 

 into the archegonium, the first period is closed, and then 

 commences the asexual generation. The embryo is 

 developed at first in the substance of the prothallus, but 

 afterwards becomes disengaged from it, and passes 

 through the different phases of its development. 

 Finally, the second generation terminates its evolution ^' ^^^' 

 by the development of the organs of multiplication as spores, which 

 always originate from a normal or modified leaf. 



Fertilisation or Fecundation in Phanerogamous or Flowering Plants. 



In flowering plants the organs of reproduction are stamens and- 

 pistils, the former representing the male element, and the latter the 

 female. The cellular pollen (sperm-cells) produced by the former 

 must be applied to the cells contained in the latter (germ-ceUs), in 

 order that the embryo plant may be formed in the seed. 



Fig. 512. Fructiflcation of Equisetum maxmnim. Great Water Horsetail, showing the 

 stalk surrounded Ijy membraoiouB sheaths, ss, which are fringed by numerous processes or 

 teeth. The fructification, /, at the extremity, is in the form of a cone bearing polygonal 

 scales, under which are spore-cases containing spores "with clavate filaments. 



