46 FIEST STUDIES IN PLANT LIFE 



scramble. Most roses have a firm stem, but many 

 of the cUmbing roses, like the white banksian rose, 

 have prickles on their long exploring branches to help 

 them to climb. The bramble also uses prickles to 

 help it to clamber over a hedge ; and as its stem is 

 less firm than the banksian rose stem, it has many 

 more prickles. 



3. Still more help is needed by the plants with 

 twining stems like the hop, the honeysuckle and the 

 convolvulus. It is a pretty sight to watch a twiner 

 that has got to the top of its pole and is throwing out 

 its etems like feelers to seek for some new support. 

 When it strikes some object it coils round it, and then 

 drags up the stem. When a high wind comes and 

 there is a heavy pull on the spiral, it acts as a spring. 

 One calls out with wonder at the beautiful way in 

 which these cables work. Some twining stems move 

 from right to left, others from left to right. " But 

 how," you ask, " can they move in a circle at aU ?" 



4. An experiment in twining. Take a long dande- 

 lion flower-stem, break it off, and press one end to 

 your tongue, and watch how it curls up. Or, still 

 better, split a long stem and place it in a saucer of 

 water. It coils up into pretty curls. If you remember 

 what we learned about the sap-tubes you will under- 

 stand this at once. We saw that the sap runs, not in 

 the skin or outer bark, but just inside the bark. It is 

 therefore the soft, inner part of the dandelion stem 

 that sucks in the water freely, and, in trying to swell 

 and lengthen, it curls round the outer skin which is 

 not swollen in this way. Now, if we have a stem with 

 one side growing faster than the other side, the same 

 thing must happen ; and this is probably what occurs 



