INTRODUCTION . 7 



which reach down from the five leaves next above. The 

 leaves are deciduous and bear buds in their axils which 

 develop in the following year. The majority of these buds, 

 however, do not develop into long shoots, but remain 

 stunted, and are called dwarf shoots. In these shoots the 

 internodes do not lengthen, so that all the leaves borne 

 by them are inserted very close together, and appear in 

 a rosette. These dwarf shoots generally bear leaves for 

 a number of years, and their age can be determined by 

 counting the whorls of dark-brown bud-scales which remain 

 attached at their bases. The dwarf shoots may, under 

 favourable circumstances, grow out into long shoots, but 

 they more commonly get left behind by the growth of the 

 tree, and when they become too much shaded by other 

 branches the shoots die and remain on the branches as 

 tufts of brown bud-scales, until they are ultimately cast, 

 off the tree. 



Internal structure of the stem. This will be described 

 in detail, as the stem forms the feeding ground for the 

 mycelia of all the most important disease-causing fungi. 

 As it will be necessary to introduce a number of botanical 

 terms which could not be explained except at great length, 

 readers who are unacquainted with the general features 

 of a plant's anatomy are recommended to omit this section 

 and pass on to the general account of larch canker in the 

 next chapter. 



If a first-year shoot, about 1-5 mmi in diameter, be cut 

 in winter and a transverse section examined under the low 

 power of a microscope, the tissues will be found to be 

 arranged as in fig. 2. On the outside are five protrusions, 

 the decuiTont leaf -bases or ' leaf -cushions ', between which 

 are narrow furrows. The cushions are nearly 1 mm. in 

 breadth and about 0-2 mm. in thickness. These cushions 

 contain rather large resin ducts, one near each edge, which 

 pass down from the leaves and end blindly in the cortex. 

 Their length is one to four times that of an internode, so 

 that any section may disclose their presence in one to four 

 cushions. Not infrequently one resin duct in a cushion is 



