19 1 7- PRAEGER — Equisditm litoralc in Ireland. 147 



central cavity as seen in cross-section (likewise intermediate) . 

 By merely pinching the stem this character can be accurately 

 tested, arvense being very resistant and feeling almost 

 solid, limosiim collapsing at once, litoralc being elastic and 

 fairly compressible. From all forms of arvense the plant 

 can be separated at once by the absence of the cyHnder 

 of thickened cells already referred to. One has only to 

 crush the stem of any arvense form to render the inner 

 cylinder at once noticeable. 



In sections of the stem, as seen under a low power with 

 the microscope, the differences stand out clearly. Miss 

 Barnes has kindly drawn (Plate VII., figs, 6, 9, 12) sections 

 of characteristic stems of E. arvense, E. limosum, and 

 E. litorale from fresh Hilltown specimens, and these figures 

 may be compared with the corresponding figures in the 

 beautiful plates of Duval- Jouve and Milde. Wliile the 

 proportions between the central cavity, the cortical lacunae, 

 and the diameter of the stem vary in all three, the essentially 

 intermediate character of E. litorale is always evident. 



EXPLANATION OF PLATES. 



PLATE VI. 

 E. morale from Rocky River. 



1. Mature fertile stem, x i. 



2. Tip of barren stem, x i. 



3. Piece of dried stem, showing slight expansion of sheaths and con- 



traction of internodes due to drying, x i. 



PLATE VII. 

 E. arvense. 



4. Joint, x 2. 5. Sheath, flattened out, x 2. 6. Section of stem, 



X 12. 



E. litorale. 



7. Joint, X 2. 8. Sheath, flattened out, x 2. g. Section of stem, 

 X 12. 



E. limosum (slender stem). 



10. Joint, X 2. II. Sheath, flattened out, x 2. 12. Section of stem, 

 X 12. 13. Ditto, showing cortical lacunae, after Duval-Jouve. 



The figures 4 to 13 are all drawn from the middle part of typical stems. 



National Library, Dublin. 



