30 



ERICACEAE 



are not, normally, completely killed by fire. (See introduction to Jepson, Manual of the Flower- 

 ing Plants of California, 6, regarding enipyroism and pyrodaptism.) 



If the Coast Ranges be considered we have even more instructive illustrations of these two 

 biological types. Arctostaphylos glandulosa is a remarkable species of the Coast Range chapar- 

 ral. It has the capacity to sprout from the root-crown after tire. The writer has frequently ob- 

 served (see page '2S, ante) that the seedlings of Arbutus menziesii produce swellings or tubers on 



the root-crown in forest where there has been 





Fig. 290. Arctostaphylos glandulosa 

 Eastw. Early stage of the formation of a woody 

 tuber on the root-crown, with a cluster of crovm- 

 sprouts. South slopes of Mt. Tamalpais, Sept., 

 1913. 



no fire during the life of the seedling. Arbu- 

 tus is closely related to Arctostaphylos and 

 points to the occurrence of the same phenome- 

 non in the latter genus. In seedlings or young 

 plants of Arctostaphylos glandulosa swellings 

 occur similarly on the root-crown in unburned 

 territory. No such expansion of the root- 

 croflTi is observable, however, in the collected 

 seedlings of Arctostaphylos stanfordiana, A. 

 manzanita, A. nummularia or any of the "fire- 

 type species," but it seems probable that 

 tubers will be found in seedlings of all the 

 "root-crown species." The young plants of 

 Arctostaphylos glandulosa, it is to be noted, 

 therefore, develop a thickened woody tuber- 

 like body on the root-crown. In the earlier 

 stages of the adult shrub the upper surface 

 of such tubers or burls resembles low disks, 

 slightly but symmetrically elevated to the 

 center, from which abruptly arise 1 or 2 to 

 several erect stems (Fig. 290). Under suc- 

 cessive chaparral fires the stems are destroyed 

 but new shoots are produced and concurrently 

 the woody tubers develop horizontally, so that 

 in the course of the centuries they become 

 broad woody platforms or burls 1 to 3 feet 

 broad, or even up to 5 or 7 feet broad. The burls bear dense masses of embryonic or potential 

 woody buds which may produce from an area as limited as a square inch a large number of shoots 

 (see description under Arctostaphy- 

 los glandulosa following). A pygmy 

 forest of stems may thus arise from 

 these platforms which become very 

 ancient (Fig. 291). This, then, is 

 an extreme type of a root-crown 

 sprouting shrub. Observation of the 

 fire-reaction habits of Arctostaphy- 

 los glandulosa have been made in 

 many parts of the Coast Ranges, but 

 especially on the slopes of Mt. Ta- 

 malpais overlooking the Golden Gate 

 (Fig. 294). 



Associated with Arctostaphylos 

 glandulosa on Mt. Tamalpais is an- 

 other shrub of marked biological in- 

 terest, Arctostaphylos nummularia. 

 It is an erect shrub, 1 to 5 feet high, 

 with a single trunk commonly % to 

 3 feet high before branching. This 

 trunk joins the main root mthout 

 enlargement ; no woody tuber or en- 

 largement is developed at ground 

 level. Under chaparral fire this 

 shrub is killed completely. On ac- 

 count of its shallow rooting it is es- 

 speeially sensitive (Fig. 292). In 

 very intense fires the shrubs of this 

 species maybe completely consumed ; 

 in fires of less intensity the shrubs 



may be killed with scant injury to the plant body. Under conditions where the course of the fire 

 is suddenly changed by the reversal or diversion of air-currents, shrubs may be killed by the high 

 temperatures generated in their vicinity without any structural injury associated with fire. Such 



Fig. 291. Arctostaphylos glandulosa Eastw. Woody 

 root-crown developing horizontally under the influence of 

 fires repeated during centuries. The erect shoots are fire- 

 killed, but subsequent to the last preceding fire new shoots 

 are developing at their bases. South slopes of Mt. Tamal- 

 pais, Sept., 1913. 



