522 ALTERATION OF FORM BY PARASITIC FUNGI. 



curious gnarled appearance; all the fibres of the root-branch thicken in a club-like 

 or tuberous manner and become twisted and entangled with one another. The so- 

 called "Fingers and Toes", caused by the Myxomycete (Plasmodiophora Brassicce), 

 is a gall-like hypertrophy on the root of Brassica oleracea, which not uncommonly 

 grows to the size of a man's head. 



Many woody plants have galls which alter the internal structure as well as the 

 outward appearance of large tracts of the stem. The parasites settle in the corti- 

 cal parenchyma, producing hypertrophy there, and afterwards the most varied 

 distortions and alterations in the wood of that region of the stem. The trunk, 

 branch, or twig becomes much swollen or knotted and the cortex rent and torn. 

 Resin or a gummy mucilage sometimes runs out of the rifts in the gall. As such a 

 parasite exercises its metamorphosing faculty for several years, the canker (as it 

 may be termed) increases in size continually. Sporangia of varied form and colour 

 appear annually on the affected places, and again disappear when they have shed 

 their spores. The part of the stem or branch above the cankerous cushion dwindles 

 and dies off sooner or later. It rarely happens that the tree or shrub is able to rid 

 itself of the parasite. Occasionally a growth of wood and cork from the adjoining 

 healthy part walls in the cankerous spot so that the parasite is destroyed. The 

 gall produced by Gymnosporangium clavariceforme on the trunks and branches 

 of the common Juniper (Juniperus communis) is an example of this form (see 

 fig. 357 x ). From the hypertrophy there project in the early spring golden- 

 yellow tongues (shown in the figure) consisting of masses of spores embedded in 

 mucilage. Other similar growths are produced on species of Juniper by Gymno- 

 sporangium conicum, G. Sabince, and G. tremelloides, but it would take too 

 long to describe their differences in detail. It is important to mention, however, 

 that each of these parasites has two stages of development, living on different 

 hosts, the hypertrophies as well as the associated spore-producing organs of the 

 parasite being different in the two cases. The "^Ecidium stage" produces carti- 

 laginous swellings (see p. 520) in definite spots on the foliage of various Pomeae 

 (Aronia, Cratcegus, Pyrus, Sorbus), the " Teleutospore stage" thickenings and 

 tuberous outgrowths on the trunks of Junipers (Juniperus communis, excelsa, 

 Sabind), and these parasites can travel from one host to the other in turn. (The 

 two stages on different hosts are shown in fig. 357; these are not of the same fungus, 

 but of nearly allied ones, and illustrate the point mentioned.) 



The parasite Peziza Willkommii attacks the trunks and branches of the Larch 

 (Larix Europcea), and produces the well-known Larch-disease or "Larch-canker". 

 The parasite having gained access at some point on the stem or branch first pene- 

 trates the cortical parenchyma, and affects the cambium so as to prevent the 

 further development of wood in that place. The development of the wood on the 

 opposite side of the stem, i.e. the formation of annual rings, may proceed for 

 several years, and in this way the attacked spot on the trunk takes the form of a 

 depression, which is rendered the more conspicuous should the wood and cortex 

 surrounding the parasite have undergone a greater thickening than usual. In 



