«9°9l 



STOKEY— ANATOMY OF ISOETES 3 l 9 



echinosp 



Ha 



m u,n vu. ^-veyi. As in the other species, the phloem forms an arc 

 in the upper part of the leaf. As the phloem is abundantly de- 

 veloped at the sides of the arc and poorly developed in the middle, 

 there is a tendency for it to separate into two lateral groups. 



Nuttallii 



other species, both in external appearance and structure. They are 

 triangular in outline, long and very slender, indeed almost thread- 



6 ' ° . i n _ a . I^>{ ^=«w in the 



like. The sporangia are extremely 



The 



sporangium region as well as above, is notably small m amount, 

 bundle, however, is well developed and larger than in any of the 

 preceding species. It differs conspicuously from those of the other 



m 



porangium and in the upper part of the leaf. Although, as in the 

 other species, the bundle becomes reduced above the sporangium, 

 there are usually eight or ten tracheids and sometimes fifteen or sixteen 

 present for a considerable distance above the sporangium, to toe 

 region above the sporangium, as in the other species, the P r °|° x >' lcnl 

 consists of large cells, which are later replaced by canals. The *a 1 

 lining the canals are heavily lignified. There is no trace of.an endo- 

 dermis, such as Scott and Hill find in I. Hystrix. The prott*) R m 

 in this region is occasionally mesarch, a few tracheids of the metax> iem 

 developing on the side toward the phloem, although the grewer 

 amount of metaxylem is alwavs on the adaxial side of the lea *V 

 it frequently forms a narrow band. In the region of the sporangium 

 the metaxylem is in the form of a crescent, with the heaviest develop- 

 ment often at the ends of the horns. In such cases the bundle tends 

 to become mesarch. The phloem also is well developed and abun- 

 dant, the sieve tubes regularly separating above the ligule in o 

 strands. A transverse sieve plate is shown in fig. n- 



H the four species are arranged in a series according to ,tte«w 

 and development of the leaf traces, the series is as follows. 1. 1 ' 



'■ melanopoda, I. echinospora var. Fleilii, I. Tuckermam var. nan ^ 

 ! * the species are arranged according to habitat, from .. terrt ; 

 ^uatic, the order would be the same, with L NuttaUn as th mat 

 terrestrial form and I. Tuckermam var. Harveyi as the m ° st J < 

 A series arranged according to the size of the leaves is as tollo -. - 



