VASCULAR CRYPTOGAMS, 



335 



GROUP IV. 



VASCULAR CRYPTOGAMS. 



Under this term are included in one group the Ferns, Equisetacese, Ophio- 

 glossacese, Rhizocarpeoe, and Lycopodiacese. As in the Muscineas, the process 

 of development is divided into two generations which are extremely different both 

 morphologically and physiologically. From the spore proceeds first of all a sexual 

 generation ; from its fertilised archegonium is produced in the second place a new 

 plant, which does not form sexual organs, but in their place a number of spores. 

 In the Ferns and Equisetacece these spores are all alike ; the Rhizocarpese and 

 Lycopodiacea?, on the contrary, produce two kinds of spores, large and small, 

 Macrospores and Microspores. 



The Sexual Generalion which is developed from the spore always preserves, in 

 Vascular Cryptogams, the form of a thallus ; it never attains, as in the more highly 

 developed Mosses, to a differentiation into stem and leaf, but remains small and 

 delicate, and closes its life with the commencement of the development of the second 

 generation. It appears, therefore, externally as a mere precursor of further develop- 

 ment, as a transitional structure between the germinating spore and the variously 

 differentiated second generation. Hence the name ProthaUium has been given 

 to this first or sexual generation of Vascular Cryptogams. 



If now the five classes are considered in the order mentioned above, the 

 remarkable fact appears — and it is one of great importance in comparing them with 

 the group that follows — that, in proceeding from the Ferns to the Lycopodiacese, the 

 development of the prothallium becomes continually simpler and its morphological 

 differentiation less pronounced. In the Ferns and Equisetaceae the prothallium 

 resembles the thallus of the lowest Hepaticse. These prothallia sometimes continue 

 to grow for a considerable time ; they contain a large amount of chlorophyll, and 

 form numerous root-hairs. After they have thus attained sufficient vigour by inde- 

 pendent nourishment, they produce the Archegonia and Antheridia, usually in 

 considerable numbers. A tendency to become dioecious is then manifested in these 

 prothallia, although they proceed from similar spores ; both kinds of sexual organs 

 being, however, often produced on the same prothallium. In the Rhizocarpeas and 

 Lycopodiaceae, on the other hand, the separation of the sexes is already prefigured by 

 the two kinds of spores, the Macrospores being female, in so far as they develope 

 a very small prothallium, which produces exclusively archegonia, or sometimes 

 only a single one. The female prothallium of the Rhizocarpese is a small 

 appendage of the macrospore, formed in its interior but afterwards developed 

 externally although nourished by it ; in Selaginella and Isoetes, which belong to the 



