2 THE TRUE GRASSES. 



Herbs, rarely shrubs or trees, with closed- jointed stems (culms) 

 and alternate, sheathing leaves. Spikelets or solitary Mowers usually 

 with empty chaff-like bracts (empty glumes; at the base, arranged 

 in panicles or spikes. 



Organs of Vegetation. — The Culm. — Grasses are either 

 nionocarpic or, more commonly, perennial by means of a 

 rhizome which is formed by the catenulate lowest inter- 

 nodes of the consecutive flowering culms and their leafy 

 basal branches. Aerial, woody, perennial stems occur 

 only among the Bambusece. Perennial grasses may usu- 

 ally be recognized by the presence of sterile shoots which 

 grow from the lowest joint of the culm or proceed from 

 that of other similar shoots ; they often break through 

 the sheath of the subtending leaf while yet buds (extra- 

 vaginal shoots) or, more rarely, develop within the 

 sheath (intravaginal). In the latter case the grass forms 

 dense and sometimes large but always isolated tufts. 

 For the formation of close turf (Grasnarbe), such as 

 the meadows of wooded regions present, only grasses 

 with extravaginal shoots are adapted, since these shoots, 

 before they grow upwards, creep for a longer or shorter 

 distance below the surface, and the runners thus formed 

 quickly fill up all the available interstices of the soil by 

 their ramifications. All grass culms branch at least 

 from the lowest nodes, and these also have the power 

 of sending out secondary roots. Even aside from the 

 richly branched Bambusece, branches from the upper or 

 from all nodes occur in many tropical grasses, but in 

 those of the temperate zone of the Old World this habit 

 is rare. The culm is rarely filled with pith (e.g., almost 

 all Andropogonece, many Panicece, etc.) ; it is usually hol- 

 low, the central cavity resulting from the separation of 

 the original pith cells which have ceased to grow, and 

 the remains of these cells line the walls of the cavity. 



Tlie Nodes. — The pith cavity is always closed at 

 the nodes which are the larger or smaller swellings 

 at the limits of the internodes. The difference be- 

 tween culm-nodes and sheath-nodes is constantly over- 

 looked, but ought to be carefully noted. The swellings 

 that are visible externally do not belong to the culm, 



