134 TH E VEGETATIVE ORGANS 



lives on as the plant, while the old one dies away. Round 

 this scar and at the lower nodes numerous fibrous roots are 

 given off in whorls (Fig. 84, 9 a.r). Similarly modified 

 stems or corms are met with in the Gladiolus. 



Ascent and descent in the soil. Contractile roots. Imagine 

 the Crocus repeating this process season after season, new 

 corms being continually formed on the top of those of the 

 previous year, and the mode of growth being a sympodium. 

 What would be the position of the corm in the soil at the 

 end of five or six years ? As each year's corm is developed 

 at a higher level than its parent, successive corms gradually 

 approach the surface. Now it is found that many under- 

 ground parts of plants have what seems to be a ' sense of 

 depth ', and if circumstances result in their being brought 

 higher or lower than their normal depth in the soil, their 

 behaviour is such as to raise, or lower, the young growing 

 shoots as required. 



The method adopted by the Crocus is one of which 

 numerous examples may be found. Fig. 84, 10 shows a young 

 corm which was developed quite near the surface of the 

 ground ; from one side a long, very thick root (c.r) grew, 

 and pushed its way deeply into the firmer ground below. 

 Its upper part then shortened and thickened, producing 

 the wrinkles seen on the surface, with the result that the 

 corm was pulled deeper into the soil. This process is 

 repeated by new roots in successive seasons until the requi- 

 site depth is reached. Such roots from their behaviour 

 are called contractile roots, and are by no means uncom- 

 mon ; they may be found in the Lily, Bluebell, Arum, 

 Dandelion, and other plants. 



Bulbs and droppers. Compare the bulb of the Tulip 

 with the corm of the Crocus. Cut a specimen longitu- 

 dinally, as in Fig. 85, 1, and note the parts of which it is 

 composed. On the outside are the smooth, membraneous 

 scale-leaves (s.i), and about four thick, fleshy leaves (s.2-5), 



