374 THE GRAMINALES 



usual localization of the growing regions also characterizes the 

 grasses which enables them to lift np again their stems if they 

 by any means become prostrate. In case the stem becomes pros- 

 trate, the stimulus of gravity causes a renewal of growth in the 

 cells at the base of the node on the side of the stem next to the 

 ground, thus causing the stem to curve up (Fig. 282, C). You 

 can easily demonstrate this peculiar localization of growth by 

 cutting off a growing stem of grass and placing it horizontally 

 with one end embedded in moist sand and noting the curvature 

 of the node after a day. The leaves show wide variation in 

 structure and are doubtless one of the factors that have enabled 

 these plants to live under a variety of conditions. For example, 

 where the plants are exposed to drought or drying winds the 

 epidermal cells are very much thickened, stomata often sunken 

 in narrow furrows and practically all species have the power of 

 rolling up the leaves in dry seasons and thus reducing the leaf 

 surface and lessening transpiration. 



The flowers are exceptionally alike in structure and show 

 about the same state of floral development. While resembling 

 those of the Typha in some particulars, they present several fea- 

 tures that indicate a decided advance over the previous group. 

 Fig. 283 illustrates the common types of inflorescence found 

 among the grasses. The flowers are arranged on elongated 

 branches, but instead of a large bract ensheathing the inflor- 

 escence (see Typha), each flower is inclosed by one or more small 

 bracts so arranged as to form a spike-like structure of over- 

 lapping bracts (Fig. 283, 2). The two kinds of sporophylls 

 may be arranged in separate spikes or on different parts of the 

 same spike, or, as in many grasses, the stamens and pistils are 

 developed in the same flower. One or more of the lower bracts 

 of a spike are usually without flowers and above them are one 

 to several flowers enclosed by secondary bracts (Fig. 283, 4). 

 Removing the secondary bracts, the flower proper is seen (Fig. 

 284, "$A, 3S). This consists in many of the grasses of three 

 stamens and one pistil and usually two small scale-like organs, 

 the lodicules, which assist by their expansion in forcing open 

 the protecting bracts at the time of flowering. The stamen con- 



