ECOLOGY 139 



former. Emmer differs from wheat in that the whole spikelet con- 

 taining several seeds becomes a fruit and breaks away from the 

 rachis entire. The seed-like fruit of foxtail millet (Chaetochloa italica) 

 and proso miUet {Panicum miliaceum) consists of a coriaceous lemma 

 and palea tightly inclosing the thin-walled caryopsis. In all these 

 cases the root breaks through the back of the lemma near the base 

 by splitting the tissue and the shoot pushes up through the space 

 between the caryopsis and the lemma, emerging near the tip. In 

 Johnson-grass (Holciis halepensis) the grain is enveloped by the 

 hard glumes and delicate lemma, sterile lemma and palea. The 

 tissue of the glume appears to be too firm to permit the root to 

 penetrate, for it passes through between the glumes. The fruit of 

 taU oat-grass {Arrhenatherum elatius) consists of 2 florets, only the 

 second of which is fertile. The root passes through the back of the 

 lemma of this floret. Rice germinates in a manner different from 

 tJiat of the other fruits described. The caryopsis is inclosed in the 

 much-flattened and keeled lemma and palea. The shoot breaks 

 through the back of the lemma at the base and appears first as a 

 pointed organ at the base of which later emerge the roots. 



175. Propagation by bulblets. — Some grasses of high 

 latitudes and altitudes produce, in the inflorescence, 

 bulblets in place of ordinary spikelets. Bulblets are 

 spikelets or portions of spikelets, in which the floral 

 bracts have been transformed into small leaves, the whole 

 becoming a vegetative shoot. These bulblets, which may 

 be provided with young roots, fall off and produce new 

 plants. A number of species may, under certain con- 

 ditions, produce bulblets, while a few do this uniformly in 

 certain regions (Poa hulbosa L.). Certain species (as Poa 

 alpina L.) are ordinarily sexual but in extremes of alti- 

 tudes and latitudes are asexual. 



PLANT SOCIETIES 



176. So far as concerns their adaptation to environ- 

 ment based upon condition of moisture, grasses may be 



