PHYSIOLOGY. 255 



by Fig. 225, 0, but the veins are parallel, as shown by Fig 

 225, p. 



In some few instances, the seeds of this class have two 

 cotyledons, in which case they always alternate with each 

 other, while in all Dicotyledonous seeds, the lobes are op- 

 posite to each other. 



Fig. 226. 



Fig. 226, represents the peculiarities of Monocotylodonous 

 vegetables. 



q. A transverse section of a Monocotyledonous stem, 

 shows that there are no medullary rays in the wood of this 

 class, nor concentric layers. 



r. Germination of a Monocotyledonous seed. 



s. A section of r, showing the cotyledon in the interioi 

 of the seed ; also the ascending stem, and the descending 

 root. 



t. Section of a germinating embryo of a grass seed, show- 

 ing the two alternate cotyledons a, b, between which is the 

 plumula, or incipient stem. 



u. The stem and leaves of a Monocotyledonous Plant ; 

 the lea v es showing the characteristic parallel veins. 



Plants belonging to this class may instantly be known, by 

 mere inspection of the leaf, as Indian corn, the Lily, and 

 Grasses, in all of which the veins run parallel, or are not 

 reticulated. 



The wood and cellular tissue, in Monocotyledonous plants, 

 are mixed together, without any distinct annual layers, and 

 the transverse sections of their stems present no radiating 

 medulla from the centre to the circumference. The leaves of 



