KUNGL. SV. VET. AKADBMIENS HANDLINQAR. BAND 55. N:0 5. 



135 



underneath, either totally disappear or become reduced to a minimum. Those bast- 

 bundles are present in P. conjmigens m. in full and in a form of 2— 5-celied strands, 

 and in P. dimorpJius at intervals and consisting of only 

 2 — 4 cells each. P. diversifoUus and P. spirilliformis m. 

 are destitute of them altogether. The endodermis of P. 

 dimorphus and spirilliformis m. has thin-walled 0-cells, 

 whereas the two other species have rather thick-walled 

 endodermis-cells and, besides, a richer sclerenchymatous 

 tissue in the central cylinder. 



The interpretation of the singular development of 

 the anatomic structure in the branches above the prim- 

 ary spike lies in the fact that those branches partly 

 must serve as peduncles, which in all these species are ex- 

 tremely short. Consequently they need an internal struc- 

 ture making them stiff like a peduncle and apt to bear 

 up the spikes. This is obtained by a coarser central cy- 

 linder with numerous free bundles and a pseudo-hypo- 

 derma along the epidermis. P. spirilliformis m., always 

 lacking the subepidermal strands as a compensation of 

 them possesses very short epidermis-cells, 2—3 times as 

 long as broad, while the other species have longer epi- 

 dermis-cells: conjungens m. about 5 times the width, and 

 dimorphus and diversifoUus respectively 5—10 and 10—20 

 times the width. 



The submersed leaves of all the species are rich in 

 lacunae but poor in sclerenchymatous tissue. 



The ligules of P. Nuttallii very much resemble 

 those of the first four species as to the membranous 

 structure, the venation, and truncate apex, but are free 

 from the leaves and open. The submersed leaves of the 

 Euhyhridi m. are sheathing and endowed with a ligule. 

 Sheaths and ligules typically connate, and like those of 

 the Pusilli connati smooth and not plicate at the back 

 as in some of the Coleogeions. After performed primary 

 function the sheath longitudinally breaks aback and thus 

 you will always find the full-grown old sheaths open. 



On account of the condition of the ligules the 

 group must be divided into two series: Euhyhridi and 

 Nultalliani. 



Fig. 60. A, B, C: P. conjungens 

 Hagstb , A, Floating leaf, nat. .size; B, 

 Top of a submersed stem-leaf, ^, C, 

 Fruit, side-view. '{'. D — /.■ P. spirilU- 

 foniiis Hagstr., D, Floating leaf ] ; E, 

 Top of a submersed stem-leaf, \''; F, 

 Transverse section of a subm. stem-leaf, 

 in, midrib, v' , lateral nerve, ?, lacunie, 

 Rtr, a faint margin.al bast-bundle, ^\^\ 



0, Diagrams of the central stele, n, from 

 a basal internode, h, a little higher up, 

 c, in the branches of the stem-prolonga- 

 tion. H, Pistil, a, ovary, h, stigma, \'*; 



1, Fruit, side-view, Y- -^C ^-^ P- (Unioy- 

 jiaits Raf., K, Top of a subm. stem-leaf, 

 ■y". /,, Fruit, side-view, 'y"; M, P. divevsi- 

 foliits Rap., Top of a subm. stem-leaf, "j". 



Series A. Euhybridi Hagstr. 



Folia suhmersa vaginata ligulata, vaginis ± connatis. Fructus rostro minimo 

 faciali. — Herbse statura graciliore. 



