RESISTANCE TO RUSTS IN HARD PINES 463 



resistant selections. I think our number 327, for instance, has very 

 heavily plugged needles. I have the impression that as the trees get 

 older, there seems to be a tendency for greater wax production, and 

 greater plugging, but there are still enough chances and enough openings 

 available for germ tubes to get in, and somehow or other, they seem to 

 find these openings. I don't think I have ever seen any evidence, how- 

 ever, that a germ tube can bore its way down through one of these solid 

 plugs. I am pretty well convinced it cannot do that, but apparently there 

 are enough cracks and crevices and openings so it can get by. Also, in 

 looking at this aspect with the scanning electron microscope, and we did 

 this for the first time last week, our view was confirmed, but we'd like 

 to know more. The plugs don't look as thick and as impenetrable as we 

 first thought, although I think as the plugs get very old a heavy, plate- 

 like covering forms on a good many of these. 



VIDAKOVIC: I studied the needle structure of European black pine 

 (P. nigra) and I found that there is a great variation on the wax forma- 

 tion within the different subspecies of this species, and also it seems 

 to me that there is a positive relation of wax formation within 1-year- 

 old needles and 2-year-old needles. Very definitely I think that, on 

 2-year-old needles, plugs are usually the case and the spores can grow 

 in. 



PATTON: You tend to confirm the findings that we have come up with? 

 Thank you. 



