444 



BOTANY 



PART II 



spermatozoids are induced to direct their motion toward the archegonia 

 by the excretion from the latter of a substance which diffuses into 



the surrounding water. In Ferns, 

 Salvinia, Equisetum, Selaginella, and 

 Isoetes, this substance is malic acid 

 or one of its salts, while in Lyco- 

 podiuin it is citric acid or its salts (^^^). 

 After the fertilisation of the egg- 

 cell by a spermatozoid there is 

 developed from it, as in the Bryo- 

 phyta, the diploid asexual genera- 

 tion ; this is the cormophj/^tic fern- 

 plant. 



The asexual generation or sporo- 

 phyte is represented by a plant 

 possessing a highly differentiated 

 internal structure, and externally 

 segmented into stem, leaves, and 

 roots. In the majority of Pterido- 

 phytes (Ferns, Eqnisetum), the fertil- 

 ised egg-cell, while still in the arche- 

 gonium, surrounds itself with a cell- wall and undergoes division, first 



Fig. 390. — Transverse section of the rliizonio 

 of I'teris arjuilina. s, Coueentrip vascular 

 peripheral bundles ; /., sclerenchymatons 

 plates ; Ip, zone of sclereneliymatous fibres ; 

 7i', coi'tex ; c, epidermis, (x 7.) 



l-'io. 'S'M. — Transverse section of stem of Li/<vpodiuin coinplanatiim. cp, Epiilerniis ; iv, fi, pp, outer, 

 inner, and innermost parts of the primary cortex, surrounding the central cylinder formed 

 by the coalescence of concentric bundles ; .sc, scalariform tracheides ; sji, annular and spiral 

 tracheides ; c, phloeni. (x:i6.) 



into two cells, by the formation of a transverse or basal wall, and 

 then into octants by two walls at right angles to each other and to 



II 



