332 BOTANICAL GAZETTE [aprii 



The next peculiarity of the stem anatomy, the absence of differ- 

 entiation into protoxylem and metaxylem in the vascular axis, is so 

 obviously related to the stunted habit of the stem that it contribute 

 nothing to a discussion of the position of Isoetes. 



In the peculiarities of the structure of its secondary wood, Isoetes 

 finds its nearest prototype in certain Lepidodendreae, as has been 

 pointed out by previous writers. The forms which present the 

 greatest similarity of structure are Lepidophloios fuliginosus and 

 dodendron obovatum. According to Scott (21) the cambium 



•P 



Lepidod 



pidophloios Jul 



arv 



secondary parenchyma only, or secondary parenchyma in which 

 are imbedded groups of tracheids. Certain species of Isoetes present 

 a close approximation to both conditions. In some species the secon - 



r j , with no well-formed 



tracheids and only a few immature tracheids. In other cases ther 

 are groups of tracheids associated with the parenchyma, and in addi- 

 tion a certain amount of immature tracheid tissue. Isoetes accor^ 

 ingly differs from these two members of the Lepidodendreae on^} ^ 

 the presence of immature tracheids in the secondary xylem. 

 not improbable that future work in the Lepidodendreae may 



to light a similar situation in that group. j 



1 ^nnimtp crrounu 



In point of anatomy, then, there seems to be no adequai 



for the separation of Isoetes from the Lycopodiales. 



The strongest argument for the establishment of a separa 



It is 



bring 



has been drawn from the gametophyte generation, in pR )ortance . 

 a multiciliate sperm. While this is a character of great linpo ^ 

 we should consider the extent of our evidence before at ac ^^ 

 much weight to it. It must not be forgotten, moreover, ^^^ 

 sperms occasionally depart from the biciliate type. ^ 



(4, P- 32) speaks of the occasional occurrence of sper ^ d(Te f the 

 cilia in Lycopodium clavatum. If we reflect that our kn0 * ° f a fcW 

 sperms of the modern genus Lycopodium is limited to ^ ^ 



inclined 



, ^ mem"-" 



more closely related Lepidodendreae, we ma> w ( | cU . rn iinin 

 regard the character of the sperms as preponderant in 



the position of Isoetes. 



