8 VINES 
the object supporting the vines. The Boston 
ivy (Ampelopsis Veitchit) is a good example of 
these disk-bearing tendril plants. It is likewise 
the only one of the type that starts to develop 
its disks before coming in contact with its 
support. 
The vines that climb by means of petioles, or 
leafstalks, are rather limited in number. They are 
interesting as showing how sensitive the natural 
organs are. If a small twig is placed so that it 
comes in contact with a petiole, the latter will ° 
start to swell almost immediately, and in a couple 
of days will have secured a firm grasp on the twig. 
Charles Darwin, in his experiments with climbing 
plants, claims to have made one of these petioles 
grasp a cotton string and entirely encircle it in 
forty-eight hours. Such sensitiveness is extraor- 
dinary when it is considered what a very slight 
irritation a cotton string would create. The 
clematis family belongs to the petiole type. 
The leaf climbers are also a very small family. 
Their habit of climbing is very simple. The leaf, 
in coming in contact with anything to excite the 
irritableness of the organ, will curl like a hook and 
then the midrib will harden and hold the plant 
fast. Most of the plants of this class are of little 
cauimercial value and my only reason for mention- 
