3<D Lang, Stele of the Shoot of Isoetes Incus tj is. 



may be regarded as applying to the genus since the 

 essential features have been found to correspond in 

 /. lacustris, I saccliarata, I foveolata, I. set ace a and 

 /. hystrix. 



The structure of the stem of Isoetes and of its stele 

 has been more or less accurately described and figured by 

 a number of investigators. Most of the facts stated below 

 are indicated in one or other of the previous descriptions, 

 but divergence of opinion exists with regard to many of 

 them and it cannot be said that the usual descriptions of 

 the anatomy of this plant are either clear or adequate. 

 An independent re-examination of the question was there- 

 fore necessary. 



As is well known, the stele of the stem of Isoetes has 

 no pith, but has a central column of xylem composed of 

 short tracheides mixed with parenchyma. The leaf traces 

 radiate from the periphery of the stele. Around the stele 

 a zone of secondary tissue, which may be referred to by 

 the non-committal name of "prismatic zone," is developed 

 centripetally from a meristematic layer. This rather ill- 

 defined secondary meristem is usually regarded as con- 

 tributing on its outer side to the cortical growth. The 

 general features just mentioned are those shown in the 

 usual figures of the stele of Isoetes and referred to in the 

 text-books. The oft-reproduced figure by Fotonie 1 may 

 be quoted in illustration. 



While the xylem of the leaf-trace is clearly continuous 

 with that of the stele there is difference of opinion as to 

 whether the phloem of the leaf-trace is continuous with 

 stelar phloem or indeed whether there is any primary 

 phlcem in the stem stele. There is further wide differ- 

 ence of opinion as to the nature of the secondary tissue 



1 "Aus der Anatomie lebender Pteridophyten." Abh. z. geol. Spez. v. 

 Prenssen. a. d. Thuring. Staat.^ VII., 1S87. 



