192 



HOW TO STUDY PLANTS. 



[LESSON 



LESSON XXXII. 



HOW TO STUDY PLANTS : FURTHER ILLUSTRATIONS. 



557. THE foregoing illustrations have all been of the first or Ex- 

 ogenous class. We will take one from the other class, and investi- 

 gate it by the Manual. 



558. It shall be a rather common plant of our woods in spring, 

 the Three-leaved Nightshade, or Birthroot. With specimens in 

 hand, and the Manual open at the Analytical Key, p. 21, seeing 

 that the plant is of the Phcenogamous series, we procyeed to deter- 

 mine the class. The netted-veined leaves would seem to refer the 

 plant to the first class; while the blossom (Fig. 366, 367), con- 

 structed on the number three, naturally directs us to the second 



class, in which this number almost 

 universally prevails. Here the stu- 

 dent will be somewhat puzzled. If 

 the seeds were ripe, they might be 

 examined, to see whether the embryo 

 has one cotyledon only, or a pair. 

 But the seeds are not to be had in 

 spring, and if they were, the embryo 

 would not readily be made out. We 

 366 must judge, therefore, by the structure 



of the stem. Is it exogenous or endogenous ? If we cut the stem 

 through, or take off a thin slice crosswise and lengthwise, we shall 

 perceive that the woody matter in it consists of 

 a number of threads, interspersed throughout 

 the soft cellular part without regularity, and not 

 collected into a ring or layer. In fact, it is just 

 like the Corn-stalk (Fig. 351), except that the 

 woody threads are fewer. It is therefore endo- 

 genous (422); and this decides the question in 

 favor of Class II. MONOCOTYLEDONOUS or EN- 

 DOGENOUS PLANTS (page 30), notwithstanding the branching veins 

 of the leaves. For neither this character, nor the number of parts in 



FIG. 36G. Flower of Trillium erectum, viewed from above. 367. Diagram of the same, a 

 cross-swition of the unopened blossom, showing the number and arrangement of parts. 



