342 MINNESOTA BOTANICAL STUDIES 



Chamacdaphnc calyciilalo, Andromeda glaiicophylla and Ledum 

 groenlandiciim. Andromeda and Cliamaedapline make their appear- 

 ance very soon after Sphagnum, so that before the latter has com- 

 pletely occupied the area, the bog heaths have appeared. By the 

 time that Sphagnum has formed a complete zone, the bog heaths 

 have developed a complete zone also. 



In the fully developed associes, Ledum groenlandiciim usually 

 appears as one of the consocies, but in some instances it does not 

 occur at all. \Mien Ledum does appear, it is at a later stage than 

 the other two. Kalmia glauca is sometimes present, but hardly in 

 sufficient quantity to be called a consocies. It is abundant north- 

 ward, and occurs rarely in other places. Either Chamaedaphne ©r 

 Andromeda may be the first successor of the pioneer Sphagnum, or 

 both may appear at essentially the same time. 



A few cases have been observed where Salix Candida, S. myrtil- 

 loides, and 6". petiolaris and Betula pumila were the first invaders of 

 the Carex associes, to be followed by the development of Sphagnum 

 and soon afterward by Ledum. It seems rather probable, however, 

 that this is a disturbance of the normal primary sequence due to the 

 partial secondary succession initiated by lumbering or flooding. 



Secondary species: Along with Andromeda and Chamaedaphne, 

 on the hummocks of Sphagnum, is usually to be found a more or 

 less extensive development of Oxycoccus macrocarpus and O. oxy- 

 coccus. The CJiamaedaphne-Andromeda associes is further marked 

 by the presence of very characteristic herbs, among which Sar- 

 racenia purpurea, Drosera rotundifoUa, and Smilacina trifolia are 

 most typical. Soxifraga pennsylvanica, Eriophorum angustifolium 

 and E. gracile are sometimes found. Menyanthes, Comarum and 

 others of the preceding Carex associes occur also. 



(6) Lari.r-Picca Associe.s 



The formation of Sphagnum mounds builds up the substratum 

 above the water-level and provides far better aeration, and thus 

 furnishes suitable conditions for the invasion of Larix and Picea, 

 which become established, and finally form such a dense growth 

 that the Chamaedaphne-Andromeda associes disappear completely. 



Consocies : There are two trees that are the typical consocies 

 in this associes, viz., Larix laricina and Picea mariana. 



Larix is the first invader of the Chamaedaphne-Andromeda 

 scrub, and in some cases may be the sole representative, except for 



