56 Dr. W. C. Williamson on 



young Lepidodendra, or were they furnished with some tem- 

 porary organ to be permanently replaced by the Stigmarise 

 at a later period ? They must from the beginning have 

 possessed some such organ capable of extracting nutriment 

 from the soil. Some living Lycopods possess a tap-root and 

 others do not. Fankhauser found one in the sporophyte of 

 Lycopodium annotinum* Treub found no such primary root 

 in the sporophyte of Lycopodium cernuum, but he observed 

 that subsequently a root was developed laterally from the 

 embryonic tubercle.f Hence the question of a primary 

 tap-root is not an unimportant one. But whatever else was 

 the case, the fact that my cabinet contains a true Stigmaria 

 not more than 6 inches in diameter shews that their set of 

 four dichotomising ones were capable of being developed 

 from the base of a very young plant. 



It is difficult to realize a sporophyte developed from a 

 prothallus of sufficiently large size to contain a primary 

 xylem strand, consisting of several thousands of tracheids 

 such as we find at the base of the arborescent stem of the 

 type of Lepidodendron Wunschianum. Then as the develop- 

 ment of this primary strand seems to have been dependent 

 upon the coalescence of an adequate supply of leaf-traces, 

 demanding a corresponding number of leaves, it is difficult 

 to realize a sporophyte, the cortical surface of which was 

 large enough to carry the requisite number of leaves to 

 furnish these leaf-traces. This difficulty raises the question 

 of what changes the sporophyte underwent to enable it to 

 bear the innumerable leaves that Solms-Laubach's hypo- 

 thesis demands. All perfect examples of the four united 

 primary roots indicate the exact diameter of the base of 

 the Lepidodendroid stem. Now we may be quite certain 

 that at their first appearance each of these four roots would 

 be in their youngest possible state, which must at least not 



*Eot. Zeitg., 1873, No. 1. 



t Ann. d. [ardin Botanique d. Buitzenzorg, 4, 1884. 



