GERMINATION AND GROWTH 



43 



be seen with the naked eye, especially if a thin longitudinal 

 section is made. It is also well seen in the water roots of the 

 common duckweed {Lemna), and on those developed by a 

 cutting of the wandering Jew, when placed in water. Are 

 there any hairs on the root cap ? Can you account for their 

 absence ? 



Note. — For a minute study of the structure of roots, see 67. 



40. Organs of vegetation. — The three parts, root, stem, 

 and leaf, are called organs of vegetation in contradistinction to 

 the flower and fruit, which constitute 

 the organs of reproduction. The for- 

 mer serve to maintain the plant's indi- 

 vidual existence, the latter to produce 

 seed for the propagation of the species, 

 so we find that the seed is both the be- 

 ginning and the end of vegetable life. 



41 . Definitions. — Organ is a general 

 name for any part of a living thing, 

 whether animal or vegetable, set apart 

 to do a certain work, as the heart for 

 pumping blood, or the stem and leaves 



Fig. 58. — Seedlings of bean 

 in different stages of growth : 

 cc, cotyledons, showing the 

 plumule and hypocotyl before 



of a plant for conveying and digesting germination; a, b d, and e, 



•^ . . successive stages of advance- 



Sap. By " function " is meant the ment. At d the arch of the 



particular work or office that an organ ^SS£ , j, .Stf Jy 



has to perform. erected itself. 



42. Seedlings of dicotyls. The bean. — Sketch, with- 

 out removing it, a bean seedling that has just begun to show 

 itself above ground ; what part is it that protrudes first ? 

 Sketch in succession four or five others in different stages of 

 advancement. Notice how the hypocotyl is arched where 

 it breaks through the soil. Does this occur in the monocotyl? 

 examined? Do the cotyledons of the bean appear above 

 ground? How do they get out? Can you perceive any 

 advantage in their being dragged out of the ground back- 

 wards in this way rather than pushed up tip foremost? 



