INJURIES INDUCED BY PLANTS 



163 



From four to eight, usually six, such mother-cells are produced 

 in each epidermal cell. These increase in size till they occupy 

 the whole space, and then divide each into four teleutospores, 

 which are arranged side by side in a palisade fashion (Fig. 93,*?). 

 During wet weather in May of the following year, each teleuto- 

 spore germinates in situ to 

 produce a promycelium (), 

 on which the sporidia deve- 

 lop on short sterigmata (c). 

 Should these reach the silver 

 fir they penetrate the young 

 leaves by means of a germ- 

 tube, and four weeks later 

 the mycelium produces two 

 rows of aecidia on the un- 

 der side of each leaf, which 

 are characterised by an ex- 

 tremely long peridium (Fig. 

 94). The peridia burst open 

 in various ways at the apex, 

 and allow the aecidiospores to 

 escape (Fig. 95). These are 

 characterised by the unusual 

 length of the intermediate 

 cells, which separate the in- 

 dividual spores from each 

 other. The aecidiospores ger- 

 minate when they reach the 

 epidermis of V actinium Vitis 

 Idcea, and produce either a 

 tube which remains of uni- 

 form thickness, though it 



FIG. 93. Epidermis and cortex of V. 

 Vilis Idiva containing ripe teltuto- 

 spores of M. Goeppertiana, some of 

 which are germinating. The mother- 

 cells, each of which forms four teleuto- 

 spores, are usually found six together 

 in an epidermal cell, a. A germinat- 

 ing teleutospore produces a promy- 

 celium, b, on which, after the formation 

 of three transverse septa, four sporidia, 

 c, usually develop on short sterigmata. 

 Magnified 420 times. 



sometimes branches, or a 

 germ-tube which enlarges in 



a sac-like fashion towards the extremity. Infection is accom- 

 plished by means of a fine hypha which springs from the germ- 

 tube. 



The infected leaves remain green for a considerable period, 

 and only fall off in the course of the summer. Even in 



M 2 



