ELEMENTS OF STRUCTURAL BOTANY. 61 



what we have already learned about the Cucumber 

 seed, we find that whilst in the latter there are two 

 cotyledons, in the present case there is but vte, and 

 this pecuharity is common to all the plants just exam- 

 ined, and to a vast number of others besides, which are 

 consequently designated Monocotyledonous plants, 

 or shortly Monocotyledons. The seeds of this great 

 Class may differ as to the presence or absence of albu- 

 men, just as the seeds of Dicotyledons do, but in the 

 number of their cotyledons they are all alike. The 

 Orchids, however, are very peculiar from having no 

 cotyledons at all. 



81. In addition to the points just mentioned, viz : 

 the number of floral leaves, the veining of the foliage 

 leaves, the usual absence of distinct petioles, and the 

 single cotyledon, which characterize our second great 

 Class, there is still another, as constant as any of these, 

 and that is, the mode of growth of the stem, which is 

 quite at variance with that exhibited in Dicotyledonous 

 plants. In the present group the increase iu the 

 thickness of the stem is accomplished not by the 

 deposition of circle after circle of new wood outside the 

 old, but by the production of new wood-fibres through 

 the interior of the stem generally, and the consequent 

 swelling of the stem as a whole. These stems are 

 therefore said to be endogenous, and the plants com- 

 posing the group are called Endogens, as well aa 

 Monocotyledons. 



We shall explain more fully the structure of exogen- 

 ous and endogenous stems, wl.en we come to speak of 

 the minute structure of plants in a subsequent chapter. 



