THE BLADE. 11 



■dichofomuni iind others, have well developed slieaths, but the 

 ))hides jiro rudimentary. 



The blades of some leaves, like those of Leersia (rice cat- grass) 

 aud Zizania (wild rice), are not quite symmetrieal, or in other 

 words, the midrib is not quite in the middle of the bl ido. 



The blades of many grasses after getting something of a start, 

 may continue to elongate or they nuiy cease to grow. In case 

 of Poa J) rate lis is (Juno grass), DacfyUs f/Ionirrata (orchard 

 grass), and many more, there seems to be scarcely any limit to 

 the length they may attain. In a damp season, when the leaves 

 were sheltered by a hedge, the writer selected a leaf of June 

 grass, still green and vigorous to the end, in which the blade was 

 five feet and four inches long. The ])lace of growth for sucli 

 leaves is a rather light green semi-circle near the ligule. The 

 tip of such a leaf-blade is the oldest i)ortion. The lower j)ortioji 

 may continue to grow as the end is cropped by cattle. 



The blade always has upper and lower surfaces unlike each 

 other. Some leaves are coiirolKfe (rolled into a cylinder), while 

 some are conihijdicate (or folded), like the two halves of a book, 

 shutting against each other. 



When Aery dry, conduplicate leaves may become convolute, and 

 between conduplicate and convolute vernation, we have all pos- 

 sible gradations passing insensibly into each other. Some leaves, 

 as those of LoUiiin riijidum, are conduplicate towards the apex, 

 and convolute towards the base. 



Leaves of many exogenous i)lants, like most of our trees and 

 shrubs, drop by separating from the stem at a natural joint, but 

 the leaves of most grasses may die, become brown and dry, and 

 still remain attached to the culm. The leaves of a few grasses, 

 as the bamboos and Sjiartiua (cord grass), have blades with an 

 articulation or joint at the base ; and some leaves have petioles, 

 418 PJtarus, Pariana, and Leptaspis, 



