SCIENCE PRIMERS. 



[vii. 



the year, when the orchis is seed-bearing, the large 

 tubercle will be found withered, and the little tubercle 

 to have grown large and plump, and have a bud at 

 its top. Still later, the whole plant dies, except the 

 smaller tubercle with its bud, which latter will grow 

 up as the orchis stem of the next year. An English 

 orchis plant is thus a travelling store of food, which 

 makes a little journey annually; but in Australia certain 

 orchises make a much longer annual journey, for the 

 new root-tubercle, instead of being attached to the 

 base of the stem close to the old root-tubercle, is 

 attached to the latter by a root-fibre sometimes six 

 inches long; and such orchises make comparatively 

 rapid marches under the ground. 



47. Adventitious Roots. Root-fibres may in 

 some cases be thrown out from the stems of plants. 



FIG. 16 Creeping stems and roots of Couch-grass. 



Such rootlets are called adventitious, and are found 

 on mature plants of both Monocotyledons (stem of 

 couch-grass near the ground), and of Dicotyledons 

 (wall-roots of ivy), and they form the supports of the 

 branches of the banyan-tree of India. 



