THE FERN'S PLACE IN NATURE. 53 



1 34. The SPERMAPHYTES include the highest of the plant- 

 world. In this group the plant-body, except in rare cases 

 (Lemna, Podostemon, etc.) is a well-developed leafy axis contain- 

 ing highly differentiated tissues of every kind; the sexual re- 

 production consists of the union of pollen-grains (male ele- 

 ment) with the embryo-sac (female element), resulting in the 

 formation of an embryo which, with its coverings, constitutes 

 the seed.* This group contains two well-marked classes t'. 

 i GymnospermcB. (Cone-bearing trees, Cycads, etc.) 

 2. Angiospermce. (All other seed-bearing plants.) 



135. It will thus be seen that the Ferns and their allies 

 occupy a high place in the plant-world, standing just below the 

 seed-bearing plants. This position they maintain not only 

 from their complexity of structure but from their evident 

 graded relation to some of the lower forms of spermaphytes, 

 especially to some that are now extinct. 



1 36. To make the relations of the various groups of pteri- 

 dophytes to each other and to the lower forms of plant-life 

 more apparent than can be done in a lineal classification, we 

 present the following outline of a possible genealogical tree : 



* It will be readily seen that this process is only a slight modification of 

 what appears in the development of the higher forms of Pteridophytes like 

 Selaginella. The prothallium, which in ferns is a marked feature, becomes 

 reduced in Selaginella, and disappears except in rudiment in the Sperma- 

 phytes. 



t The above is in accordance with the older botanical systems. The com- 

 parative and morphological study of the higher plants is leading us on to a 

 more natural system of classification than that which is given in the ordinary 

 Manuals of Botany. The day of artificial groups like the " Apetalous division 

 of Exogens" is long since passed. This is not the place to discuss these 

 changes, but this note is given merely to call attention to the progress in a 

 field where many have been led to believe there was no further progress 

 possible. Among the many transitional systems the following ought to 

 be accessible in almost any good library: Engler-Prantl : Naturlichen 

 Pflanzenfamilien, n, pp. 1-5, and Macmillan : The Metaspermae of the 

 Minnesota Valley, pp. 18-29. 



