SECT. xin. MONOCOTYLEDONOUS STEMS. 385 



after having formed the ribs and footstalks of the 

 leaves, enter the upper part of the stem, approach 

 towards its centre, bend down for a short distance, 

 then turn towards the exterior, interlace with the 

 bundles of the previous year, which have followed a 

 similar course, and make a circle of rough marks on the 

 surface of the stem. The stem then increases in length, 

 and a new plume of leaves crowns its top ; the same 

 process is repeated ; and, as this goes on indefinitely, the 

 lower part of the stem is rough, and sometimes even 

 rugged, as that of the Palmyra palm. In consequence 

 of this manner of growth, a perpendicular section of a 

 stem shows a series of curves intersecting each other 

 and originating in points gradually ascending as the 

 palm grows in height. These curves proceed from every 

 point of the circumference of the stem, present their 

 convexities to the centre, and bend round, and enter the 

 leaves, which are long, lanceolate, and often pinnate with 

 veins running through them longitudinally. In some 

 palms the greater part of the centre of the trunk is 

 altogether cellular tissue, but each species has an ar- 

 rangement of its own. Some palms, as the date palm, 

 are dioecious, one plant bearing male, the other female 

 flowers. In these cases, the pollen is carried from one 

 tree to the other by the wind or by insects, and, as 

 much is lost in the transit, there is always more produced 

 than is required to fertilize the female flowers. 



The Graminacese are very numerous, but the general 

 structure is virtually the same, whether it be a simple 

 herbaceous grass, a sugar cane, or a bamboo. The stem 

 of the grasses is jointed, and furnished with long lanceo- 

 late leaves, springing alternately to the right and left of 

 each successive joint, and the parts of the stem between 

 the joints are embraced and nearly surrounded, as by a 

 sheath, with the expanded bases of the leaves ; for, in 

 this class of plants, one growth always springs from 



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