Buds and Stems. 63 



reserve food materials, and in this position survive the 

 winter. 



In the spring the terminal shoot produced from a bulb 

 grows vertically upward (d) and sends forth leaves and 

 flowers ; while at a node a short distance below the sur- 

 face of the mud, roots are formed, and also buds, from 

 which the horizontal shoots arise, thus bringing us back to 

 the stage at which we began the cycle. This example is 

 an exceedingly instructive one in showing how plants may 

 employ any force acting in a definite direction (in this case 

 gravity), not in impelling all of its parts in one direction, 

 but as a fixed line from which may be determined the 

 various directions toward which its different members 

 should grow. It is also instructive in another way : it 

 shows that plants are not inert bodies, but are possessed 

 of a high degree of sensibility which enables them, in a 

 certain sense, to perceive their condition and the forces 

 within whose range they are lying. Notice, for instance, 

 that the horizontal shoots of Sagittaria do not grow indefi- 

 nitely in the horizontal direction, but after a suitable dis- 

 tance from the parent plant has been traversed so that 

 danger of crowding is avoided, they turn upward and pro- 

 duce leaves and roots. So, too, the downward-growing 

 shoot, having reached a depth where the winter may be 

 passed in safety, turns upward and produces the bulb to 

 which is intrusted, as well as to the seeds, the life of suc- 

 ceeding generations. 



46. Light as Guide. Where gravity cannot be employed 

 as a guide in achieving certain results, light may be used 

 instead. If the stem has a climbing habit and is supported 

 by lateral outgrowths in the form of suckers or roots which 

 are able to obtain foothold on walls, trees, etc., the shoot 

 employs the line of propagation of the greatest incident 



