CRYPTOGAMS AND PHANEROGAMS. 243 



indusium of the Hjmenophyllaceae, certain Cyatheacese (Fig. 

 212 E), and Salvinia (Fig. 218) ; that they are really homologous 

 with these is probable, but is not proven. Some authorities 

 regard them as structures found only in the Phanerogams. 



The ovule is thus a " monangic " (i.e. reduced to 1 sporangium, 

 the nucellus} sorus, situated on afunicle, and enclosed by one or two 

 cupular indusia, the integuments. Some of the ovules are erect 

 (prihotropous) , others curved (campylotropous) , the majority reversed 

 (anatropous) (Fig. 249). 



[Goebel (1884 and earlier) with Strasburger considered the entire ovule of the 

 Phanerogams as homologous with the macrosporangium, the integuments how- 

 ever, as new structures in contradistinction to the Ferns : the funicle then corre- 

 sponds to tbe stalk of the sporangium. The integuments of the ovule (according 

 to Goebel, 1-582) differ from the indusium of the Fern-like plants in being devel- 

 oped from the basal portion of the nucellus and are not, as in the Ferns and 

 Isoetes, a portion (outgrowth) of the leaf which bears the sporangia (K).] 



The nucellus is the only macrosporangium which never opens; 

 the macrospore remains enclosed in it, and the macrosporangium remains 

 attached to the mother-plant. It is therefore essential that the 

 method of fertilisation which is employed should be very different 

 from that of the Cryptogams. The pollen-grains must be transferred 

 to the ovule, and retained either by a drop of mucilage at the micro- 

 pyle (Gymnosperms) or by the stigma on the carpels (Angiosperms). 

 Fertilisation by spermatozoids, which are ciliated and freely 

 motile has been discovered in the Cycadese and in Ginkgo. 



Many other modifications, unknown in plants of more simple 

 structure, take place, for instance, in the shoots which bear the 

 fertile leaves; especially in the form of the stem or thalamus (hypo- 

 gynous, perigyrious, epigynous) ; in the development of the peri- 

 anth which stands in intimate connection with the special means 

 employed to effect fertilisation ; with respect to the different 

 grades of union found in the leaves ; in the union of the flowers 

 into aggregations of a higher order (inflorescences), and at the same 

 time the production of " floral-leaves " (page 235). 



The sexual generation. The Fertilisation. 



The sexual generation in the Mosses is relatively well developed, 

 because not only the protonema, but all the other vegetative 

 parts of the Moss-plant, in addition to the archegonia and anther- 

 idia, belong to it. In the groups which follow, a gradual but in- 

 creasing reduction of the sexual generation takes place, and at the 



