26 



BOTANY 



PAET I 



be superfluous, as the Dodder does not produce its own nourishment, but 



derives it from its host plant. Cuscuta Trifolii, one of the most fre- 

 quent of these parasites, is often the cause of 

 the large yellow areas frequently observable 

 in the midst of clover fields. In certain tropi- 

 cal parasites belonging to the families Piafflesi- 

 aceae and Balanophoraceae, the process of re- 

 duction has advanced so far that the flowers 

 alone are left to represent the whole plant. 

 Rafflesia Arnoldi, a plant growing in Sumatra, 

 is a remarkable example of this ; its flowers, 

 although they are a metre wide, the largest 

 flowers in existence, spring directly from the 

 roots of another plant (species of Cissus). 



A peculiar form of metamorphosis is ex- 

 hibited by some climbing plants through the 

 transformation of certain of their shoots 

 into tendrils. Such tendrils assist the 

 parent plant in climbing, either by twining 

 about a support or otherwise holding fast to 

 it. The twining bifurcated tendrils of the 

 Grape-vine, for example, are modified shoots, 

 and so are also the more profusely branched, 

 hold - fast tendrils of Ampelopsis Veitchii 

 (Fig. 27). 



Shoots may undergo a still greater re- 

 duction by their modification into thorns, 



as a defence against the depredations of animals. Of shoots modi- 

 fied in this manner, the Black Thorn (Prunus 



spinosa), the White Thorn (Crataegus), and the 



Honey Locust (Gleditschia) afford instructive 



examples. The thorns are simple or branched, 



hard, pointed bodies. In Gleditschia (Fig. 28) 



the thorns are developed primarily from the 



uppermost of several serial buds ; while 



secondary thorns may develop on older por- 

 tions of the stem from the lower buds of 



the series, and thus give rise to clusters of 



thorns. 



The most marked change in the form of 



the shoot, in addition to the displacement and 



union of its different members, takes place in 



phanerogamic flowers. The shoots from which pia 



flowers are developed are termed floral 



shoots, in contrast to the foliage shoots, 



the functions of which are merely vegetative. 



27. — Ampelopsis FeUchii. 

 , R, Stem-tendrils. (J nat. 



schiu 

 size.) 



Stem-thorn of Gleclit- 

 triucanthos. (£ nat. 



The axis of the floral 



