ON STEMS 39 



in English ; in our country these two classes of plants 

 retain the denomination given them by Linnaeus, of mon- 

 ocotyledons and dicotyledons. 



Caroline. These are hard sounding names, Mrs. B. : 

 I hope their explanation will render them intelligible. 



Mrs. B. I believe you will find no difficulty in under- 

 standing them. The class of plants whose stems grow 

 internally, and are by us denominated monocotyledons, 

 are distinguished by their seed, which, during germina- 

 tion, is converted into a thick leaf, yielding nourishment 

 to the young plant until it is strong enough to suck it up 

 from the soil. This leaf is called a cotyledon, and the 

 epithet mono, which signifies one, implies that this class 

 of plants have a single cotyledon. 



The other class, whose stems grow externally, and are 

 called dicotyledons, comprehends all those plants whose 

 seeds in germinating split into two parts, forming two 

 nutritive lobes or seminal leaves ; and hence they bear 

 the name of dicotyledons, which signifies two cotyledons. 



Emily. I have seen lupins, peas, and beans germi- 

 nate in this way ; but do not recollect having observed 

 any seed germinate with only one cotyledon. 



Mrs. B. They are much less common in these cli- 

 mates, at least in plants of sufficiently large dimensions 

 for their cotyledons to be observable. 



There is a third class, denominated acotyledons, which 

 have no cotyledons and no vascular system, such as 

 fungi, lichens, &c. ; but of these we shall not treat at 

 present. 



Let us first examine the structure of the stems of the 

 monocotyledons or endogenous plants. Of this descrip- 

 tion are the date, the palm, and the cocoa-nut tree, the 

 sugar-cane, and most of the trees of tropical climates. 



Their stems are cylindrical, being of the same thick- 

 ness from the top to the bottom ; whilst those of Europe, 

 you know, always become more slender and taper to- 

 wards the summit of the tree, approximating to the con- 

 ical form. 



169. How by Linnseusl 170. What explanation is ^iven of the 

 term monocotyledons'? 171. What explanation of the dicotyledons'? 

 172, What plants are named of the latter class 1 ? 173. What is a 

 third class, and by what name are they called 1 ? 174. What plants 

 and trees are endogenous or monocotyledons'? 175. What is the 

 form of their stemsl 



