I9I9] 



WA TERM A N—ROOT S Y STEMS 



43 



Mycorrhiza. — The question of symbiotic fungi suggested itself 

 early in the investigations, but there was no opportunity for a 

 detailed study. Slight examination of a few species was made, 

 but did not show evidence of the presence of such fungi. 



Enlarged root tips. — ^A frequently observed feature of many of 

 the dune species was the marked enlargement of some root tips. 

 The tip rapidly increased to 3 or 4 times its normal diameter and then 

 gradually tapered away again, the extreme length of the enlarge- 

 ment being 20-30 times its greatest diameter. This enlargement 

 seemed to be confined to the central tip of the larger branches only, 



Fig. 14. — Primus piimila plants in sandy morainic substratum 



and especially in those which showed a marked and rapid extension 

 into new territory, for which reason the name ''pioneer" or invad- 

 ing root tip has suggested itself for this type. It was found under 

 apparently normal conditions both in pure sand and in humus, but 

 in the sand it seemed to be increased in some species by the chemical 

 solutions used, and even by distilled water. The largest tips found 

 were in the case of Juncus balticus, where in shape and size they 

 resembled large angleworms. It was not possible to make a 

 microscopic examination of fresh material, but sections of tips 

 preserved in 4 per cent formaldehyde showed no signs of symbiotic 

 fungi or animal forms. The enlargement seemed to be due to 

 increase in size and number of the parenchyma cells. 



