8 4 



PLANT BIOLOGY 



arrangement, see all sedges. For 5-ranked (which is one 

 of the commonest), see apple, cherry, pear, peach, plum, 

 poplar, willow. For 8-ranked, see holly, osage orange, 

 some willows. More complicated arrangements occur in 

 bulbs, house leeks, and other condensed parts. The buds 

 or "eyes" on a potato tuber, which is an underground stem 

 (why ?), show a spiral arrangement (Fig. 1 1 1 ) 

 The arrangement of leaves on the stem is 

 known as phyllotaxy (literally, " leaf arrange- 

 ment "). Make out the phyllotaxy on six 

 different plants nearest the schoolhouse door. 

 In some plants, several leaves occur at one 

 level, being arranged in a circle around the 

 stem. Such leaves are said to be verticillate, 

 or whorled. Leaves arranged in this way are 

 usually narrow: why? 



Although a definite arrangement of leaves 

 is the rule in most plants, it is subject to 

 modification. On shoots that receive the 

 light only from one side or that grow in dif- 

 ficult positions, the arrangement may not be 

 definite. Examine shoots that grow on the 

 under side of dense tree tops or in other par- 

 tially lighted positions. 



'*> 



. ^ 



FIG. in. 

 PHYLLOTAXY 

 OF THE PO- 

 TATO TUBER. 

 Work it out 

 on a fresh 

 long tuber. 



SUGGESTIONS. 55. The pupil should match leaves to determine 

 whether any two are alike. Why? Compare leaves from the 

 same plant in size, shape, color, form of margin, length of petiole, 

 venation, texture (as to thickness or thinness), stage of maturity, 

 smoothness or hairiness. 56. Let the pupil take an average 

 leaf from each of the first ten different kinds of plants that 



: meets and compare them as to the above points (in Exer- 



;e 55) and also name the shapes. Determine how the various 

 eaves resemble and differ. 57. Describe the stipules of rose, 



>le, fig, willow, violet, pea, or others. 58. In what part of 

 the world are parallel-veined leaves the more common ? 59. Do 



