3922-23. j HOTANICAL SOCIETY OF EDINBURGH 167 



becomes wedge-shaped, as seen in fig. 0. In the case of P. 

 mirabilissima, the teleutospore pedicel is packed iu tightly 

 between the iiredospore pedicels, and the swelling of the base 

 of the former produces pressure in the sorus which causes the 

 teleutospore, together with its persistent pedicel, to be 

 violently shot out. This process can be readily observed 

 under the microscope when sori removed from leaves which 

 have been kept for a short time in dry air are mounted in 

 water. 



The introduction of P. mirabilissima into Scotland probably 

 took place comparatively recently, for it is hardly conceivable 

 that this conspicuous rust can have existed for a long period 

 in the neighbourhood of Edinburgh without being observed. 

 Berberis AquifoUa was introduced into this country from 

 America in 1823, and is now extensively grown in gardens and 

 shrubberies. It is easily reproduced and it is improbable that 

 living plants have been brought in from that continent in 

 recent years. From the known facts, it seems unlikely that 

 the rust was introduced on this host. It may have been 

 introduced on some other species of Berberis and subsequently 

 spread to B. AquifoUa, but again there is no evidence for this. 

 The introduction of living spores on the surface of plants not 

 belonging to any of the host species is also a possibility. 

 Shrubs and trees, especially conifers, are brought into the 

 country in fairly large numbers, and there is no doubt that 

 numerous living fungal spores are introduced on these. The 

 occurrence of the rust in two situations which are over 20 

 miles apart suggests that its spread may now take place rapidly, 

 and the common occurrence of the host plant will undoubtedly 

 facilitate its distribution. 



Observations on the Leaf of Senecio gonocladus, 

 ScH. Bip. By Dorothy G. Wilson, M.A., B.Sc. 



(Read 21st December 1922.) 



A native of the Cape region of South Africa, Senecio 

 ■gonocladus is a distinct xerophyte, characterised especially 

 by the succulence of its cylindrical leaves, which measure about 

 one inch in length and are covered externally by a coating 

 of wax. 



