90 



spring certain plants send up rusted leaves as their first growth. 

 The leaves are punctate first with tiny, sticky spermogonia; 

 then between the spermogonia there develop the flower-like 

 cluster-cups of aecidiospores. Even with the heavy spore pro- 

 duction the leaves remain green but there is sufficient toxic 

 action to stimulate greater growth with abnormal results. The 

 leaves are smooth instead of downy, the blades are reduced in 

 size and stand stiffly erect on long petioles. Blossoms are few 

 on an infected plant; instead of blossoms a set of normal leaves 

 follows the rusted ones; the rusted ones die off by the end of 

 May and the rust, hidden in the rootstock, is seen no more 

 until next spring. (52) I have watched the recurrence of rust on 

 these same plants for half a dozen years but there has been no 

 infection of the other Hepaticas. The aecidiospores need an 

 alternate host, the plum or cherry for their growth. I have made 

 this cross infection in the planthouse but I allow neither plum 

 nor cherry near my bank of Hepaticas. 



It is intriguing, although perhaps futile, to speculate over 

 the choice of hosts by these rusts which require a change of host 

 for the completion of their life cycles. A chance wind may ex- 

 plain the transfer of spores but there seems, in the dissimilar 

 hosts, no common character by which to explain such limita- 

 tions. (40) The contrast in hosts is particularly striking in the 

 case of the rusts of coniferous trees. Aecidiospores from rust on 

 the larch infect willow. When we explore the shores of the Res- 

 ervoir, left dry in the autumn, we find the willow leaves pep- 

 pered with yellow clusters of teleutospores for the larch. The 

 seemingly wayward fancies of the cedar rusts have been men- 

 tioned. The spruce rust at least chooses a perennial evergreen 

 from among the herbs at its base. The blister rust of the white 

 pine, however, jumps to currant and gooseberry for its teleuto- 

 sporic stage. 



Here is another immigrant from Europe. In 1906 it was 

 found in a plantation of white pine seedlings which had been 

 imported from Germany; at about the same date it was found 

 on imported white pine seedlings in other New England states 

 and in New York. Its eradication has now become a forestry 

 problem. The government, in an attempt to save the valuable 

 white pine, has undertaken to eradicate the currant tribe, the 

 lesser host. With the currant link removed, an infected pine 



