ANATOMY 29 



is arranged on this plan, but in most there are several 

 strands, and in many ferns the number of anastomos- 

 ing strands is very large. In none of the living ferns 

 are these primary strands united by any secondary 

 growth of woody tissue. In the Lycopods the arrange- 

 ment, though with individual peculiarities, is much like 

 that in the ferns. So long as only living forms were 

 studied, it was thought that the formation of secondary 

 wood was a character only developed in the Gymno- 

 sperms and the flowering plants. Since the anatomy 

 of the fossils has been studied, however, the remark- 

 able fact has come to light that in the early and extinct 

 forms of the ferns and the Lycopods, and even of the 

 Equisetaceae, secondary woody tissue was developed 

 in considerable quantities, and apparently on the same 

 plan as is now found in the Gymnosperms. Their 

 primary structures were like those of their living re- 

 presentatives, and quite unlike the higher plants. It 

 is almost universally true that the primary structures 

 of the plant are the truest guides to its affinity. The 

 development in time past of the secondary wood in 

 the Lycopods and other extinct Pteridophytes was at 

 a time when they were among the largest tree-like forms 

 of plants then extant. To support their mighty shafts and 

 to supply their crown of leaves with water it was necessary 

 to have additional woody tissue, which was developed 

 in the most straightforward and simplest way in radial 

 rows of cells. That Lycopods to-day do not develop 

 such wood is doubtless due to the fact that they do not 

 grow to such a size as to require it. But, when we ask 

 why we do not now find them growing to such a size, 

 we have left the province of anatomy and entered the 

 philosophical field in which uncertainty still reigns. In 

 the families below the ferns there is little that greatly 



