SUMMARY 363 



SUMMARY OK THE COMPARATIVE EXAMINATION OK THE 



LYCOPODIALES. 



The sporophyte of the Lycopodiales has now been studied compara- 

 tively as regards its external form, its spore-producing members, its 

 anatomy, and embryology. The conclusion arrived at from all these 

 quarters is favourable to a strobiloid origin, with subsequent specialisation 

 along lines variously divergent. By the comparison of known representa- 

 tives of the Lycopodiales, living and fossil, certain characters have been 

 recognised as relatively primitive, others as derivative : and thus a general 

 idea has been obtained of a primitive type of Lycopod-sporophyte, which 

 forms the basis of a theory how such a sporophyte came into being. In 

 form this primitive sporophyte was probably a simple, unbranched, radially 

 constructed shoot, endowed with unlimited apical growth, while local 

 intercalary growth might also occur. The axis bore undifferentiated leaves, 

 each of which had one sporangium associated with it in a median position. 

 It was rooted at its base, but the origin of the root may be held 

 to have been accessory in evolution, as it is seen to be late and variable 

 in the individual development. The internal construction of the shoot 

 showed a non-medullated monostele, continuous as a cauline column to 

 the apex of the axis, while the foliar strands were inserted with but slight 

 local disturbance upon its periphery. Its sporangia were kidney-shaped, 

 and not greatly extended radially. The primitive body thus sketched in 

 its broad outlines was derived from a spindle-shaped embryo, without 

 any haustorial swelling, or tuberous protocorm. The theory of the 

 strobilus, as enunciated in Chapter XI., would adequately account for 

 the origin of so simple a sporophyte as this, from a still more primitive 

 body, with sterile base and fertile apical region, by segregation of the 

 fertile tissue into separate sporangia, and by enation of sporophylls. 



The nearest living representative of such a sporophyte which has been 

 adequately investigated is Lycopodium Selago ; but it is to be remembered 

 that this is the only one of 39 species of the Se/ago-section of the genus 

 so examined, and there are indications, derived as yet from external 

 characters only, that other and more primitive types than L. Sclago exist 

 among them : these await further investigation. The first leaves formed 

 on the embryo of L. Selago are lateral in origin, and become aerial and 

 green, but are sterile : sporangia were noted by Bruchmann, 1 as first 

 appearing after the second branching of the axis, which, however, is 

 early as compared with the other European species, though not as 

 compared with the large Andean forms. Their early appearance, as 

 well as the similarity of the sterile and fertile leaves, coupled with 

 the evidence of abortion of sporangia in the upper region, all point 

 to the conclusion that originally all the leaves were sporophylls, while 

 all arose laterally upon the axis. 



1 /..i. . p. ioo. 



