188 



HOW TO STUDY PLANTS. 



|_LESSON 31. 



p. 12, the student is led to ask, first, is the plant PELENOGAMOUS 01 

 FLOWERING ? Of course it is ; the blossom, with its 

 stamens and pistils, answers that question. Next, to 

 which of the two classes of Flowering Plants does it 

 belong ? If we judge by the stem, we ask whether it 

 is exogenous or endogenous (422-424). A section of 

 the stem, considerably magnified, given on page 15L 

 361-4 we may here repeat (Fig. 362) ; it plainly shows a 

 ring of wood between a central pith and a bark. It is therefore 

 exogenous. Moreover, the leaves are netted-veined, though the 

 veins are not conspicuous. We might even judge from the embryo; 

 for there is little difficulty in dissecting a flax-seed, and in finding 

 that almost the whole interior is occupied by an embryo with two 

 cotyledons, much like that of an apple-seed (Fig. 11, 12), and this 

 class, as one of its name denotes, is dicotyledonous. If we view the 

 parts of the blossom, we perceive they are five throughout (Fig. 363, 

 365), a number which occurs in that class only. All these marks, 

 or as many of them as the student is able to verify, show that the 

 plant belongs to Class I. EXOGENOUS or DICOTYLEDONOUS PLANTS. 



543. To which subclass, is the next inquiry. The single but 

 several-celled ovary in the centre of the flower, enclosing the ovules, 

 assures us that it belongs to the ANGIOSPERMOUS subclass, p. 13. 



544. To get a good idea of the general plan of the flower, before 



proceeding farther, cut it through the middle lengthwise, as in Fig. 

 364, and also take a slice across a flower-bud, which will bring to view 

 an arrangement somewhat like that of Fig. 365. Evidently the 

 blossom is regularly constructed upon the number five. It has a 

 calyx of five sepals, a corolla of five petals, five stamens, and five 



FIG. 382. Section of the stem of Flax, magnified. 363. Summit of a branch of the common 

 lax, with two flowers. 364. A flower divided lengthwise and enlarged. 



