176 ANNALS OF SCOTTISH NATURAL HISTORY 



Turning now to the more specialised types of Dicoty- 

 ledons, we find that of some families almost every member 

 is liable to bear galls, while in others only certain genera are 

 attacked, or only a few species of different genera may be so. 

 Among the Rosaceae we meet with numerous galls, the work 

 of very various makers. Some of these are of low organisation, 

 while others in their complexity of structure and in their 

 aspect recall the highly specialised forms of oak-galls. The 

 Cruciferae, Leguminosae, Rubiaceae (as represented by the 

 Bedstraws and their allies), and Compositae may be men- 

 tioned as families including many herbaceous plants that 

 bear galls. Among the more highly organised woody 

 Dicotyledons, the Limes, Maples, and Common Ash are rich 

 in galls, though seldom of complex structure. 



Few families of Dicotyledons, even in the British flora, 

 except some of those represented by only one or by very 

 few species, are absolutely free from galls ; and, if we look to 

 the records from other countries, we see that a good many of 

 our plants bear galls elsewhere, though they are not yet 

 known to do so in the British Islands. Among the few 

 that are not yet recorded as gall-bearers may be noted the 

 families of the Water-lilies, Holly, Crowberry, Sundews, 

 Water Milfoils, Ivy, Thrift, Bladderworts, and Bog Myrtle, 

 along with a few other less conspicuous types. Several of 

 these are water-plants, and others show peculiarities of 

 nutrition that may protect them against the gall-makers. 

 But it is difficult to suggest a sufficient cause why most of 

 these families should be free, while others, apparently as 

 secure against attack, are gall-bearers. The immunity of so 

 many of the Monocotyledons is even more difficult to explain, 

 e.g. the freedom from galls of Orchids and of Cyperaceae 

 (apart from a few Carices) in contrast with the relatively 

 numerous galls on Grasses. 



Every part of plants, from the rootlets upwards, is 

 liable to be galled ; but in each plant certain parts are 

 usually more liable than others. Most gall -makers show 

 a preference for a definite part ; for example, some attack 

 the roots alone, others the leaves, others the flowers, or 

 even a single organ of the flower, such as the seed-vessel. 

 A few parasites produce changes that show themselves 



