LESSON 22.] FORMATION OP THE EMBRYO. 



139 



whole course of vegetation (12, &c.). So, in attempting to learn 

 how this growth took place, it will be best to adopt the same plan, 

 and to commence with the commencement, that is, with the first 

 formation of a plant. This may seem not so easy, because we have 

 to begin with parts too small to be seen without a good microscope, 

 and requiring much skill to dissect and exhibit. But it is by no 

 means difficult to describe them ; and with ^he aid of a few figures 

 we may hope to make the whole mat- 

 ter clear. 



383. The embryo in the ripe seed 

 is already a plant in miniature, as we 

 have learned in the Second, Third, 

 and Twenty-first Lessons. It is al- 

 ready provided with stem and leaves. 

 To learn how the plant began, there- 

 fore, we must go back to an earlier 

 period still ; namely, to the forma- 

 tion and 



384. Growth of the Embryo itself. 

 For this purpose we return to the 

 ovule in the pistil of the flower (323). 

 During or soon after blossoming, a 

 cavity appears in the kernel or nu- 

 cleus of the ovule (Fig. 274, o), lined 

 with a delicate membrane, and so 

 forming a closed sac, named the 

 embryo-sac (s). In this sao or cav- 

 ity, at its upper end (viz. at the 

 end next the orifice of the ovule), 

 appears a roundish little vesicle or 

 bladder-like body (v), perhaps less 

 than one thousandth of an inch in 



diameter. This is the embryo, or rudimentary new plant, at its 

 very beginning. But this vesicle never becomes anything more 

 than a grain of soft pulp, unless the ovule has been acted upon by 

 the pollen. 



FIG. 328. Magnified pistil of Buckwlieat ; the ovary and ovule divided lengthwise ; some 

 pollen on the stigmas, one grain distinctly showing its tube, which penetrates the stylo, re- 

 appears in the cavity of the ovary, enters the mouth of the ovule (o), and reaches the sur- 

 face of the embiyo-sac (a\ near the embryonal vesicle (u). 



