1916-17.] BOTANICAL SOCIETY OF EDINBURGH 163 



may be of different species. In a phylum such as that of 

 Irroratum the indumentum in most of the forms is con- 

 structed on the same lines, but that does not keep us from 

 recognising specific segregation amongst the forms based 

 upon other diagnostic characters. At present we are only 

 on the threshold of the study of indumentum in Rhodo- 

 dendron. In the example of this Irroratum series with 

 which I am dealing I see differences in the punctulations 

 of the mature leaves which I have no doubt would add to 

 the sum of differential characters of the species had one 

 only time and eyes to follow out an investigation of them. 

 This will be one of the necessary tasks of a future mono- 

 grapher of Rhododendron. Meanwhile Mr. H. F. Tagg, 

 Assistant in the Museum of the Royal Botanic Garden, 

 Edinburgh, is devoting some time to the study of the 

 forms exhibited by the indumentum in Rhododendron, and 

 has obtained some interesting results. I had hoped, having 

 the advantage of the co-operation of Mr. R. M. Adam, 

 Assistant in the Studio here, whose skill as a photographer 

 is unrivalled, to have been able to provide a series of 

 illustrations from microspecimens of typical forms of 

 indumentum, and many of them have been prepared, but 

 he is now doing more valuable work in serving the guns, 

 and who shall say that our intention will reach fruition. 



It may not be amiss to mention here that most of these 

 species of the Irroratum series seem to be infested by a 

 fungus which sends out upon the under leaf-surface in 

 particular small black rod-like conidiophores, upon which 

 conidia are seldom seen, except under shelter of the midrib. 

 These conidiophores look like solitary black setae upon a 

 small black cushion, and must not be confused with real 

 appendages of the Rhododendron itself. Large black spots 

 and tubercles of fungal origin are also abundant sometimes 

 upon the leaves. 



Turning now to the inflorescence and flower of the 

 Irroratum series. 



The typical form of the inflorescence is a compact globular 

 truss of many flowers arranged on usually short pedicels 

 one centimeter or under long in Rh. adenoste^nonuon, 

 Rli. ceraceum, Rh. eritiinuin, Rh. gymnanthuni, Rh. 

 lukiangense, Rh. pogonostylum, Rh. spanotrichum ; in the 



