296 



IONOCOTYLBDONS. 



wall of the one-chambered ovary. The real stalk, at the base 

 of the ovary, is very short ; the long inferior ovary makes a 

 long flower- stalk unnecessary, as it pushes out the flower and 

 exposes it to visiting insects. A curious point is that the 

 ovules are not formed until after pollination has taken place. 

 Compare young and mature flowers to see the twisting of the 

 ovary, which brings the labellum to the front. 



Trace the shoot down, below the inflorescence and the 

 leaves, to the basal swelling, which is a root-tuber. Cut the 

 tuber across and test the cut surface for starch. Besides 

 the tuber in which the present year's shoot ends, notice the 



BUD 



-|- STEM B 



,ROOT BUD" 



SHEATH. 

 TUBER. 



LEAF' 



Fig. 116. Orchis. A, Base of a Plant (dug up in summer), with old (1) and new (2) 

 Tubers ; B, Section of a developing Tuber. 



brown and shrunken tuber formed last year, and the new 

 tuber being formed for next year. To see these tubers of 

 different ages and to trace their life-history you must of 

 course examine plants at different times of year. 



Each year one root (sometimes two), instead of growing 

 out like the other roots, becomes swollen up and packed with 

 food (made by the green leaves and transported downwards 

 through the stem) ; this root is formed at the base of a bud, 

 from which next year's leaf- and flower-bearing shoot will 

 develop (Fig. 116). When the shoot dies, the root- tuber, 

 with the bud above it, remains in the soil during winter, and 

 the early growth of the shoot takes place at the expense of 

 the food stored in the tuber, while ordinary roots grow out 

 to absorb water and salts from the soil. 



