BUDS AND STEMS 



119 



A tuber. 



Note the stems growing from 

 the eyes at one end. 



IT- ^^^Y^l^^ ^ ^^^^?. potato./ Notice the marks or eyes on its surface. 



Find a little projection withm each eye. This is a bud. Immediately under 



It you will find a tmy scale which represents a leaf. Later we shall see that 



a bud on a stem always has the same 



relation to a leaf as does this bud to the 



tiny scale. In other words, the position 



is the same in each case, and the struc- 

 ture may be said to be homologous to 



that of the bud and leaf of an ordinary 



stem. 



Try to find out the arrangement of 



the leaves on the potato; they may be 



either opposite or alternately placed on 



the stem. See, also, if you can find the 



point at which the stem was attached 



to the parent plant. 



If a potato is cut in cross section it 



will be possible to find all the parts of 



a stem. The pith occupies the central 



portion; around this is the wood, which here looks hke a dark band. Out- 

 side the wood we find the cortex, the potato being protected by the rather 



delicate epidermis. 



Cut a potato and a sweet potato in cross 

 section; place each in red ink overnight. 

 It will then be easy to compare the course 

 taken by fluids in passing up a root and a 

 stem. 



Cut out several eyes from healthy pota- 

 toes. From one or two remove all of the 

 flesh of the potato, and in the other speci- 

 mens leave food supply intact. Does the 

 stored food help the young plant in its 

 growth ? Test for food stuffs in the potato. 

 What foods are present? 



Reduced Stems. — In some plants the 

 stem is so reduced as to be almost lost. 

 This may be of a distinct advantage to the 

 plant in enabling it to escape destruction 

 from enemies. Such a plant is the common 

 dandelion, which, because of its short stem, 

 escapes grazing animals and the knives of 

 lawn mow^ers. Many other low-lying weeds 

 are partly immune from dangers which be- 

 set taller plants. 

 Bulbs. — In bulbs the stem is covered with thickened leaves, the whole 



making a compact and reduced plant which, because of its stored food, 



enables the plant to make an early start in the spring. 



Cut an onion in longitudinal sections; draw, showing the scalelike, 

 thickened leaves, the greatly reduced stem, and the roots. Test for food 

 stuffs. What foods do you find present in the onion ? 



» See Hunter and Valentine, Manual, page 29. 



Longitudinal section of a lily bulb. 

 Note the much thickened leaves, 

 and the flower cluster at the 

 center. Photographed by 



Overton. 



