10 



FIRST SUBDIVISION. 

 VASCULAR CRYPTOGAMS. 



The Vascular Cryptogams include all the highest forms of cryptogamic 

 life, and constitute a well-marked group of plants intermediate between 

 the Gymnosperms, or lowest division of Flowering Plants, and the lower 

 or Cellular division of Flowerless Plants. From the former they differ 

 mainly in the mode in which fertilisation is effected ; from the higher 

 forms of the latter in the much greater differentiation of tissues. The 

 term ' vascular ' Cryptogams is, however, strictly speaking, correct only 

 to a limited degree. Although the arborescent and fruticose species 

 display as well-marked a differentiation of their tissues as Flowering 

 Plants, into epidermal tissue, ' vascular ' bundles, and fundamental tissue, 

 and the bundles consist of distinct xylem and phloem (without any 

 intermediate cambium, as in Gymnosperms), it is only rarely, as in that 

 group of Flowering Plants, that the xylem is composed of vessels in the 

 true sense of the term. 



The Vascular Cryptogams and the highest families of Cellular 

 Cryptogams are distinguished from Flowering Plants by an obvious 

 Alternation of Generations between Sexual Generation or Oophyte^ and 

 Non-sexual Generation or Sporophyte. The former is a small and 

 purely cellular structure, usually of very temporary duration, the purpose 

 of which is to bear the sexual organs of reproduction, male antherids 

 and female archegones, the structure of which is uniform in all essential 

 characters throughout the class, and which are borne on a cellular ex- 

 pansion, \hQ prothailium. This prothallium may be either monoecious 

 or dioecious — that is, the male and female organs may be borne on the 

 same or on different prothalHa. The act of fertilisation consists in the 

 impregnation of an oosphere, a naked mass of protoplasm contained 

 within the central cell oi the archegone, by one or more a?itherozoids, 

 minute masses of protoplasm endowed with spontaneous motion by 

 means of vibratile cilia, which escape from the cells of the antherid 

 and penetrate to the central cell of the archegone. The immediate 

 result of the impregnation of the oosphere is that it invests itself 



