T4 INTRODUCTION TO BOTANY 
narrow at the base and wider at the tip, as in the evening prim- 
rose, so that nearly all the space between the leaves is filled in. 
During which year of the life of a biennial is its principal 
work photosynthetic? During which year is it reproductive? 
Fig. 57. The wild frost grape, a 
typical tendril climber 
This vine is climbing on an American 
elm. The height up to the branch Z 
is about 60 feet, and the average cir- 
cumference of the main vine, 3 feet. 
Redrawn and simplified from a pho- 
tograph by Robert Ridgway 
Why are beets, carrots, parsnips, 
and salsify used as food at the 
en of the first season’s growth ? 
72. Leaf mosaics. Any combi- 
nation of leaves (whether found 
in rosette plants or on longer 
stems) in which the space is very 
fully occupied, with few spaces 
between the leaves, is called a 
leaf mosaic. Walls covered with 
Japanese ivy furnish beautiful 
examples of leaf mosaics on a 
large scale, and many of our 
common house plants illustrate 
the same phenomenon. In any 
leaf mosaic many of the leaves 
occupy a very different posi- 
tion from that which they would 
have taken if borne on a vertical 
stem. 
73. Climbing into the light. 
Many plants, of very diverse 
families, secure a better expo- 
sure of the leaves to light by 
climbing. The principal types 
of climbing plants are four in 
number: scramblers, like the common climbing roses; root 
‘Timbers, like the poison ivy (fig. 56) and the English ivy 
(fig. 40); teniners, like the morning-glory ; and tendril climbers, 
like the grapevine. The only way in which one can get a 
thorough knowledge of the behavior of climbers is to watch 
them throughout as much as possible of the growing season. 
