GYMNOSPORANGIUM. 393 



Woernle investigated the anatomical changes induced by the 

 various Gymnosporangia frequenting the twigs and needles of 

 Juniperus communis. In the needles the mycelium lives inter- 

 cellularly, at iirst outside the endodermis, but later also penetrating 

 within this. The sporogenous cushions originate on the upper 

 surface of the leaf to right and left of the middle nerve, 

 where the stomata occur and hypoderm is absent. At these 

 places a cushion or stroma of pseudoparenchyma is produced 

 and ruptures the epidermis (Fig. 226). This however is at 

 once healed over by a cork-formation round the margin of the 

 cushion, again to be ruptured as the latter increases in size, 

 once more to be healed by cork-formation, and so on. In 



FlQ. 226. — Comparison of (a) uoiiual Juniper-needle with one (&) bearing teleuto- 

 spores of Gymnosporangium. In tt the double outline indicates the hypoderm ; 

 the central vascular bundle and an underlying r.esin-canal are shown. (After 

 Woernle.) 



this way a corky layer is formed under the sporogenous cushion 

 and gradually displaces it. If in a following year the cushion 

 be again formed, the scar is ruptured and heals as before. 

 Needles frequently remain in position for two, three, or four 

 years, but most of them fall off in the first autumn. Under 

 the sporogenous cushion the cells of the mesophyll increase 

 both in number and size. 



In considering the twig-deformations, Woernle distinguishes 

 the form assumed by the Gymnosporangium on the needles, as 

 just described, from a form which inhabits the thicker twigs. 

 Both cause deformation of twigs, but their effects differ as follows: 

 "The needle-inhabiting form can only cause a slight swelling 

 . extending almost regularly round the whole twig ; the twig- 

 inhabiting form, on the other hand, always gives rise to a very 



