226 HOWARD E. PULLING 



and roots branching at right angles to the plane of the paper are 

 omitted except as noted in the text. Several trees, ranging in 

 size from those a few decimeters high to mature trees, were 

 examined in various kinds of habitats, deviations from the type 

 shown in the figure being noted in the text. 



Black Spruce. {Picea mariana (Mill.) BSP; P. nigra Link; 

 P. brevifolia Peck.) — This tree is the common inhabitant of the 

 muskegs. As indicated in the figure it is very shallow rooted 

 even when growing in deep soil. For example, on a well drained 

 slope with a south exposure, sjtuated on a large island at the 

 entrance of the Nelson river into Split lake (about 56°23'N. lat. 

 and 96°25'W. long.) the soil was not frozen above a depth of 

 170 cm. The first 6 cm. w^ere moss and leaf mold; the next 25 

 cm. a brown clay that was flocculated and very dry except in the 

 upper 4 or 5 cm.^ At 150 cm. a heavy clay was encountered 

 that was solidly frozen at 170 cm. In this soil the black spruce 

 roots were not found below 7 cm. although willow and white 

 spruce roots were found at a depth of 80 cm. 



Four possibilities immediately present themselves in this and 

 the cases following that deal with shallow^ rooted plants: (1) 

 The roots do not penetrate the flocculated clay because it is dry. 

 (2) They do not penetrate it because it is cold. (3) They do 

 not penetrate it because of its low oxygen content. (4) They 

 do not penetrate it because the shallow root-habit is inflexible. 

 Considering these briefly it may be stated that the last is the 

 most probable because (1) black spruce is shallow rooted in a 

 well aerated, sandy soil which is more moist below the roots 

 than about them (Brule river region). This also applies to (3). 

 (2) Changes in soil temperature with depth cannot be effective 

 for the temperature in the 6 cm. of moss and leaf mold was 37°F. 

 and there was no observed change until within a few centimeters 



- This dry, flocculated soil is of general occurrence in all the region examined 

 and there is additional reason to believe that its presence is very widespread. 

 Even when occurring under deep layers of sphagnum saturated with water it is 

 usually dust dry, so that plants may be actually growing in a dry soil when the 

 surface indications point to the existence of a bog. For a more complete descrip- 

 tion and an hypothesis of origin see Pulling, H. E., Some unusual features of a 

 subarctic soil. Johns Hopkins Circular, pp. 188-190. March, 1917. 



