ON THE STRUCTURE OF BUDS 123 



gates greatly, and becomes twice bent, as shown in 

 the figure, so that the leaf remains erect. This arrange- 

 ment is, so far as I know, unique. 



In the Passion Flower (Passiflora racemosa) the 

 stipules are large, foliaceous, and developed far in 

 advance of their own leaves, so that each pair enclose 

 their own leaf, the simple tendril in its axil, and the 

 younger portion of the bud. Proceeding from the out- 

 side inwards, the stipules change considerably, being 

 first ovate, gradually becoming smaller, then lanceolate, 

 and finally subulate. In some other species of Passi- 

 flora the stipules more or less completely protect the 

 bud, and the petioles are terete, and are provided with 



glands. 



In by far the greater number of cases, however, 

 stipules protect the younger leaves only. 



In the Willows, as we have already seen, the sti- 

 pules develop late, and the bud is protected by a pair 

 of modified leaves. In the allied genus, Populus (the 

 Poplar), on the contrary, the stipules develop early, and 

 to them the protection of the bud is entrusted. 



In the Black Poplar (Populus nigra) the terminal 

 bud (fig. 191) is conical and somewhat angular. 



The first arid second pairs of scales (fig. 192), form- 

 ing part of the terminal bud, are stipules belonging 

 to leaves that developed during the previous summer 

 and fell in autumn. They only cover, however, a 

 part of the bud. They are the hardest of the 



