Jan., 1919] Effects of the Eruption on Vegetation 201 



of carrying the over-extended tops and roots of the old trees. 

 This is very conspicuous in many places where the Alaska 

 willow (Salix alaxensis) grew among the poplars. In the 

 course of three years the willow practically made good its 

 losses and was as thrifty as ever, while the poplars were more 

 dead than alive. 



In places where the ash, after lying on the ground for some 

 time, has been washed away by streams, exposing the buried 

 parts of such trees, the difference between the willows and 

 poplars is very striking. The dead poplar trunks stand as they 

 were at the time of the eruption, but the willows have grown 

 extensive systems of new roots. These are not distributed 

 throughout the length of the buried stem but are almost con- 

 fined to the region immediately beneath the former surface of 

 the ash. (See page 202.) The advantage of the willow over the 

 poplar is obvious. That these new roots were really the decisive 

 factors in the survival of the willows is shown by numerous 

 cases where trees which had survived burial had succumbed to- 

 the removal of the ash layer, with the consequent dislocation 

 of the new roots. 



This type of root reaction was not confined to the willows- 

 but was found in a number of other plants as well. In general 

 it may be stated that the stems of buried plants either remained 

 unchanged, or reacted in this manner, developing the char- 

 acteristic two-storied root system. The plants in which this 

 reaction was found were: Salix alaxensis, Salix nuttallii y 

 Salix glauca, Echinopanax horridum (see page 188), Calama- 

 grostis langsdorfii, Betula rotundifolia (feeble), Rubus specta- 

 bilis, V actinium ovalifolium, Deschampsia ccespitosa. 



STEM REACTIONS. 



The reactions of the aerial parts of plants remain to be 

 considered. For the most part the new growth gives no indica- 

 tion that unusual conditions were introduced in burial beyond 

 those incident to the merely mechanical action of the ash. 

 But a few species show interesting reactions to burial. The 

 most conspicuous case is the pussy willow (Salix nuttallii). 

 Before the eruption this grew as an erect bush two or three 

 meters tall. In many cases all parts above the ground were 

 killed in the eruption, but new shoots have been put out from, 

 the surface of the ash. These show no tendency to form new* 

 branches like the original trunk, but spread out flat on the 



