Holm, Some new anatomical characters for certaia Gramineae. 119 



of thick-walled mestome-parenchyma in the larger bundles bet»veen 

 the leptome and hadrome. In M. disticliophylla the cells of the 

 mestome-sheath show an excessive thickening in comparison with 

 the other speeies, and the companion-cells of the sieve-tubes are 

 veiy thick-walled in M. gracillima. Viewed in transverse section 

 the outline of the mestome-bundles is either oval {M. disticliophylla) 

 or orbicular {M. gracilis and gracillima). Besides these two types 

 of leaves exhibited by Muhlenbergia, there is still a third one, 

 characteristic of M. ßlijoes Curtis, and which has been described 

 by Mr. Kearney (1. c.). The leaf of this speeies is permanently 

 conduplicate and has deep furrows on either face of the blade. 

 The mestome-bundles are located in the very prominent ribs, and 

 are almost embedded in a large mass of colorless tissue occupying 

 the ventral ridges over the larger mestome-bundles, besides that 

 it occms as forming layers on the dorsal face of the leaf-blade. 



Lycurus Kth. 



L. phleoides H. B. K., which is also a member of the 

 ^Stipeae", was collected on dry plains near Manitou, Colorado, 

 and represents a type that has structural characteristics in common 

 with other Gramineae of similar habitat, 



The leaf is conduplicate, furrowed, and both faces are very 

 scabrous with numerous short, thick-walled papillae, and there are 

 long, pointed hairs scattered over the upper face. Stomata occur 

 on both faces near the shallow furrows and are level with the 

 epidermis. Intervening between the ribs are small groups of bulli- 

 form cells, which border on a few rows of colorless-tissue, exten- 

 ding to the dorsal epidermis. The stereome is represented by a 

 large group on the lower face of the midrib, and a similar large 

 one on each leaf-margin; otherwise this tissue occurs only as a 

 lew cells on either face of the ribs. — The mesophyll consists of 

 palisades arranged radially around the mestome-bundles, these 

 again being surrounded by a thin-walled, green and large-celled 

 parenchyma-sheath and by a mestome-sheath, which shows a very 



Mr. Kearney*) does not attribute a mestome-sheath to any of these 

 speeies since the vessels in the smaller bundles were observed to border 

 directly on the parenchyma-sheath. Having followed the study of these 

 speeies we concluded with Mr. Kearney that the more or less completely 

 closed sheath of thick-walled cells, which lie up to the parenchyma-sheath, 

 were not to be considered as belonging to a mestome-sheath, but that they 

 simply represented mestome-parenchyma. But since we now studied other 

 speeies of Muhlenbergia and from very different localities we have arrived 

 at the conclusion that the three speeies actually possess a mestome-sheath. 

 Moreover by renewing tue examination of M. capillaris we have found that 

 the interruption of the mestome-sheath by the small vessels varies somewhat 

 between apex and base in the same leaf, and that there are many eases in 

 which even the smallest bundles possess a completely closed inner sheath. 

 Testing the sheath with concentrated sulphuric acid it shows the same power 

 of resistanee that is usually characteristic of true mestomesheaths, hence we 

 infer that Muhlenbergia capillaris possesses both a parenchyma-and a mestome- 

 sheath. 



*) Kearney, Thomas H., The plant eovering of Ocracoke Island. 

 (Contrib. U. S. Natl. Herb. Vol. V. No. 5. p. 285. Washington 1900.) 



8* 



