FUNGUS-GALLS ON STEMS. 



521 



colour takes its place, so that orange spots appear on the surface of the foliage, 

 contrasting vividly with the green of the unaltered portions of the leaf. 



Galls rising from sharply defined parts of the stem are comparatively rare. 

 One of the most remarkable is produced on the stems of a Laurel (Laurus 

 Canariensis) by the parasitic Exohasidium Lauri. When it appears above the 

 bark it looks like an aerial root, but rapidly grows into a branched spongy body 

 8-12 cm. long similar in appearance to one of the Fungi belonging to the family 

 Clavarieae (of. fig. 195^ p. 21). The galls produced by Entyloma Aschersonii and 

 Magnusii on the Composites Helichrysum arenarium and Gnaphalium luteo-alhum 



Fig. 357.— Fungus-galls. 



1 Gall on the stem of the Juniper (Juniperus communis) produced by Gymnosporangium clavariceforme. 2 Gall on the leaves 

 of Aronia rotundi/olia produced by Gymnosporangium conicum. 



take the form of outgrowths, varying from the size of a pea to that of a walnut, 

 developed from special spots on the root. Whether the spherical tubercles growing 

 on the root-fibres of many Leguminosse, especially those of the Bird's-foot Trefoil 

 {Lotus corniculatus), the Fenugreek (Trigonella foenum-grcecum), Lady's-Fingers 

 {Anthyllis Vulneraria), Lupin {Lwpinus variabilis), and the Liquorice (Glycyrrhiza 

 glabra) are to be regarded as true galls caused by the Bacteria -like organisms 

 invariably to be found in their interior is questionable. According to the most 

 recent investigations they are the outward expression of a case of symbiosis and 

 not of pure parasitism. 



Gall developments which involve whole roots or rootlets are found on the Alder 

 {Alnus glutinosa), and on the Cabbage {Brassica oleracea). The gall which is 

 produced on Alder roots by Frankia Alni attains the size of a walnut and has a 



