6 THE TRUE GRASSES. 



cessive shoots are autidrom [a technical term of German 

 morphologists], that is, if the first leaf of one falls to the 

 left of the subtending or supporting leaf, that of the next 

 falls to the right, etc., so that the first leaves of all 

 branches fall on the same side of the main axis. The 

 same holds true, of course, in case of secondary branches 

 rising from the axils of these leaves even when the sub- 

 tending leaves are undeveloped, as is usually the case in 

 the inflorescence. 



Every foliage leaf consists of at least two parts, the 

 sheath and the blade. A true petiole is inserted be- 

 tween these only in a few broad-leaved, tropical grasses 

 (Pharus, Phyllorachis, some Ischcema, many Bambusece, 

 etc.). The blade is always absent in hypophyllia and 

 prophylla, and in the floral leaves (called glumes or 

 bracts) it is either absent or transformed into a narrow 

 bristle-shaped appendage, the awn, which is sometimes 

 twisted or bent. The sheath surrounds the culm like a 

 tube, and the two edges usually overlap in front, the 

 covering edge being somewhat raised. In the successive 

 interuodes the raised edge is alternately on the right and 

 left. The sheaths of numerous grasses (all Sesleriece, 

 many Poce [pratensis L., trivialis L., alpina L.~\, Bromus 

 [inermis Leyss., erectus Huds.], Briza, Melica, Dadylis, 

 Glyceria ftuitans Brown, etc.) are, on the contrary, per- 

 fectly closed, but the young and still included inflo- 

 rescences, by forcing their way upward through these 

 narrow channels, usually cause them to split. The 

 sheath matures earlier than the internode above its in- 

 sertion, and consequently its stiffening tissues, viz., the 

 sclerenchyma bundles, are perfectly formed at the time 

 when the enclosed interuode in its basal portion is yet 

 tender and without firmness. The sheath is, in con- 

 sequence, a very important protection for the young in- 

 ternodes, and this function is performed even by the 

 blade! ess first leaf in breaking through the ground with 

 its hard point ; if the latter be cut away, the enclosed 

 shoot is not able to stand upright and reach the surface. 



The Ligule. At the point of union between the blade 

 and sheath there is at the inside an erect prolongation 



