92 PRACTICAL COURSE IN BOTANY 
ing of the rhizome gives rise to the tuber, of which the 
potato and the Jerusalem artichoke are familiar examples. 
Can you give any evidence to show that the potato is a 
Fic. 106.— Potato tuber shi 
cels, A, A, or pores for air on the surface; the eye? (100.) Do the 
S, leaf scale, or sear. 
owing lenti- 
modified stem? Find the 
point of attachment of the 
“. tuber to its stem and stand 
+S it on this end, which is its 
“A. natural base. Notice that 
the eye sits in the axil of 
the little scale that forms 
the eyelid. What does the 
scale represent? What is 
scales occur in any regular 
order — that is, opposite, or alternating with, each other, like 
the leaves on a stem? 
Look on the surface for a number of 
small, lens-shaped dots (A, A, Fig. 106) scattered irregularly 
over it. These are aérating pores called lenticels, and are 
found in most dicotyl 
stems. Does _ their 
presence help to throw 
light on the real nature 
of the tuber? If any 
sprouts occur on your 
specimen, where do 
they originate? Where 
do buds and sprouts 
originate on plants 
above ground? Make 
a sketch of the outside 
of a potato, showing 
the lenticels, eyes, and 
scales, or the scars left 
107 
Fries, 107, 108,— 
Transverse and longi- 
tudinal sections of the 
potato: A, skin; B, 
cortical layer ; C, outer 
pith layer ; D, inner pith 
layer. 108 
B 
A 
by the scales in case they have fallen away, as has probably 
happened, if your specimen is an old one. 
Cut a small slice from the stem end of two potatoes, stand 
