The Science of Plant Growing 29 



fly till dissolved, when the juices are reabsorbed. A stone or other object 

 would cause the infolding of the tentacles, but if such objects contain no 

 nitrogen the tentacles soon unfold, without having produced any chemical 

 changes in the protoplasm, thus proving that nitrogen was the element 

 of food required. 



Climbing" Plants. The Convolvulus, Wistaria, and Scarlet Runner are 



123 4 



Fig. 11. To show contraction induced by the contact of insects. Tentacles on Leaf of Sun-dew (Drogera) 



1, Glands at the extremity of a Tentacle; x 30. 2, Leaf with all its Tentacles inflexed towards the middle. 

 3, Leaf with half the Tentacles inflected over a captured insect. 4, Leaf with all the Tentacles extended. 

 2, 3, and 4x4. 



examples of plants that climb by twining their stems round some support- 

 ing object. If the top or free end of a Scarlet Runner is observed at 

 different times during the day, after it has commenced to run, it will be 

 seen to be swinging round in a wide circle, and should it chance to touch 

 a stake, string, wire, or other support, it commences immediately to coil 

 tightly round the same and to make rapid progress. The stem is sensitive 

 to contact and this sensitiveness resides in the protoplasm, being one of 

 its properties. Scarlet Runners grown in the field without stakes often 

 twine round one another, but without proper support they never attain 

 the length of which they are capable, nor do they produce so heavy a 

 crop. The saving of labour and the extra cost of stakes are the chief 

 reasons for this method of culture. Sweet Peas, garden Peas, Cucumbers, 

 Melons, Vines, and others climb by special structures known as tendrils. 

 The leaf stalks of Clematis and Tropseolum twist round supporting objects 

 in a similar fashion, and they as well as tendrils are sensitive to contact. 



[J. F.] 



4. THE ROOT AND ITS WORK 



The Primary Root. The first structure that emerges from the interior 

 of a germinating seed is the primary root or radicle, which goes perpen- 

 dicularly down into the earth. If the minute structure of the tip of this 

 is examined it will be seen to consist of very small square cells at and 

 behind the growing point (fig. 12). Around and in front of this is a layer 

 of brick -shaped, corky cells, most of which are empty and dead. This is 



