328 



Dansk Botanisk Arkiv, Bd. 3, Nr. 1. 



highly interesting plant seems to have been gathered in a season 

 where the plant had stopped its growth, as no young branches or 

 summits of thallus are to be found in the material brought home. 

 Therefore I am able, to give only a rather fragmentary description 

 of the construction of this plant which Falkenberg just mentions. 

 On the other hand, Falkenberg gives a very detailed description 

 of the old world species, Dictyurus parpiirascens. 



Dictyurus occidentalis forms dense tufts, up to 10 cm or more 

 and is fastened to the substratum, rocks, stones etc. by means of 

 small discs and rhizoids growing out from the basal part of the stem. 

 This often very irregularly shaped base, from which new erect stems 

 arise, grows together with bases of the neighbouring plants forming in 



this way rather large tufts. From this basal part 

 the erect more or less branched shoot-systems 

 arise. These are mostly bare in the lower part 

 bearing merely the remaining basal parts of 

 the aside-pushed free ends of the branch- 

 systems of which the plant is constructed. These 

 remnants are found alternately and distichously 

 on both sides of the terete stem. Higher up we 

 find the characteristic reticular tissue origina- 

 ting from the upper ends of the pushed 

 aside free branches of the sympodium sur- 

 rounding the central stem like a closed spiral 

 staircase. A transverse section of the stem shows four pericentral 

 cells surrounded by a thick cortical layer (Fig. 329). 



As Dictyurus occidentalis, with regard to the fully developed 

 tissue, bears such a close resemblance to Dictyurus purpurascens I 

 feel quite convinced that its development takes place in a very 

 similar way. In Dictyurus purpurascens we have, as described by 

 Falkenberg, sympodial growth of such a kind that the branch which 

 constitutes the continuation of the main axis is developed upon the 

 second segment of the mother branch, giving in this way two seg- 

 ments to the sympodial stem. Besides this first branch whose pur- 

 pose is the continuation of the sympodium, the branch pushed aside 

 bears yet three side-branches. These three branches are sympodially 

 ramified so that each branch-system bears only a single side-branch, 

 namely that intended for constituting the continuation of the axis. 

 This branch is placed upon the second segment of the mother branch 



Fig. 329. Dictyurus 

 occidentalis J. Ag. 

 Transverse section 

 of the main stem. 

 ■ (About 60:1). 



