SECTION II 



PHANEROGAMIA 



The Transition from the Cryptogams to the Phanerogams. — The 



old names, Cryptogams and Phanerogams, are here retained jiartly on 

 historical grounds and also because there are no lietter and equally 

 short terms for the two great grades of the vegetable kingdom. The 

 sharp distinction which formerly appeared to exist between the two 

 groups has, however, as our knowledge has advanced, become less 

 marked. The Phanerogams appear as a continuous development 

 from heterosporous Vascular Cryptogams. The recognition of this 

 is owing, in the first place, to the work of W. Hofmeister (^). 



It has been seen (p. 425) that the existence of an alternation of 

 generations is an essential character, common to both Bryophytes and 

 Pteridophytes ; the life-history exhibits a regular alternation of a 

 sexual with an asexual generation. While in the Bryophyta only 

 the sexual generation attains an independent existence, in the 

 Vascular Cryptogams this stage appears as the inconspicuous pro- 

 thallium. The asexual generation, ou the other hand, which in the 

 Moss was represented by the sporogonium dependent throughout its 

 life on the sexual plant, becomes physiologically independent in the 

 Pteridophyta. In them it appears as the conspicuous plant, the Fern 

 or Horsetail, and bears leaves, on some of which (the sporophylls) 

 the sporangia develojD. A shoot bearing a numlier of sporophylls, 

 and frequently with other leaves forming an outer investment, is 

 known as a FLOWER. Thus Hquiseium (Fig. 408, p. 460) affords a 

 good example of a flower of simple construction, iti which the 

 sporophylls are all alike. 



Tlie appearance of heterospory (p. 44G) marks a most important 

 advance ; the sexual differentiation, which in homosporous forms did 

 not appear until the sexual generation (prothallium, gametophyte) is 

 evident in the asexual plant (sporophyte). The sporojjhyte produces 

 male sporangia (the microsporangia) and female macrosporangia. The 

 function of the sexual generation is limited to the production of the 

 male or female sexual organs, and it undergoes still further reduction. 

 In the germination of the microspores only a single, vegetative pro- 



475 



