62 



Introduction to Botany. 



the soil are directed upward by gravity, this is by no means 

 always the case. Certain underground shoots of the po- 

 tato, for instance, are directed 

 downward at various angles, 

 and the underground shoots of 

 the goldenrod are guided in a 

 horizontal direction. In Sagit- 

 taria variabilis we find an in- 

 teresting example of 

 somewhat diverse 

 habits. Radiating in 

 various directions 

 from the parent plant 

 (m, Fig. 23) are hor- 

 izontal underground 

 shoots (g) t which 

 finally turn upward 

 at the apices (//) and 

 produce leaves 

 above the surface. 

 Roots are produced 

 at the basal node of 

 the upright shoots, 

 which then become 

 independent indi- 

 viduals (z). Later in 

 the season, under- 

 ground shoots (/) 

 are produced which 

 grow vertically 

 downward for about 



a foot, and then turn upward at their apices for a short 

 distance and form bulbs (e) that become filled .with 



Sagittaria variabilis. d, last year's tuber, from 

 which the central plant (m) has sprung; g, off- 

 shoots from m\ h, terminal bud of g, which has 

 turned upward and will produce a plant like i ; 

 f, offshoot which has grown down into the mud 

 and will produce a tuber similar to e, which is a 

 tuber of the current season destined to survive the 

 winter and then produce a new plant, as d has 

 done. 



