FACTORS INFLUENCING REPRODUCTION 



845 



The roots of the transplants in the flats showed at the end of the 

 growing season some remarkable effects of soil differences. The most 

 striking effect was upon the period of root growth. At the end of 

 October, more than two months after the growth of the shoots had 

 ceased, the roots of all three species — spruce, fir, and white pine — were 

 still functioning on the raw humus. This was shown by the abundance 

 of small, translucent growing tips characteristic of roots at the height 

 of the growing season. These growing tips were absent on the mild 

 humus and mineral soil, except for the fir rootlets on the mild humus 

 in contact with the wood of the flat. This exception seems to indicate 

 that the wood of the flat had the same effect in favoring continued 

 absorption as the forest litter composing the raw humus. Further evi- 

 dence of the value of organic material just beginning to break down is 

 seen in the propensity of both spruce and fir rootlets for growing 

 through cones and twigs. The indications are that spruce and fir on 

 their natural soils, the raw humus of the forest, maintain the power of 

 root absorption for a large part of the year, if not for the entire year, 

 in such a way that they are able to take advantage of brief intervals of 

 warmth to absorb water. This is in accordance with the researches of 

 Resa,^^ who found that a root growth in conifers persisted through the 

 year except for a rest period in January and February, and of Peter- 

 son, ^^ who found that root elongation in Picca excelsa, Finns montana, 

 and Larix decidua may begin in February and continue to November. 

 Gates^^ found that the ericads are capable of conducting moisture with 

 a temperature as low as 15° C. 



The different soils also brought about differences in the character of 

 the roots. The spruce roots in the raw humus resembled those grow- 

 ing under natural conditions in the forest, having the characteristic 

 brown color and dense branching, while those of the same species in 

 the mild humus were black, were considerably less in diameter, were 

 not quite as much branched, and had a large proportion covered with 

 a white fungus mycelium. The mineral soil had the poorest spruce 

 roots, much less branched than those on the raw humus or mild humus 

 and with less growth in length ; consequently with much smaller root 

 area. Many of the root tips were covered with a white mycelium which 

 appeared to be the same as that found in the mild humus. The thick- 

 ness of the roots was intermediate between those of the raw humus 

 and mild humus. 



" Quoted by Brown, H. P., in "Growth studies in forest trees." Bot. Gaz., 

 Vol. 59. No. 3, PP- 19.V241, 1915. 



" Gates, F. C. : "Winter as a factor in the zerophily of certain evergreen 

 ericads." Bot. Gaz., 57, pp. 445-489. iQM- 



