THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 65 



buds. When these are fully formed (about May), growth for the 

 year practically ceases. In Adenostoma the procedure is exactly the 

 reverse. This species begins its activity with the formation of its 

 vegetative shoots, and its flowers, borne on these, open in June and 

 close the period of active growth. All agree in making the fullest 

 utilization of the relatively short period when both moisture and 

 temperature conditions come nearest to combining for the general 

 good, i. e., in the spring months, when soil-moisture is still abundant 

 and air and soil temperatures are on the increase. April, in the 

 Palo Alto region, is the month of greatest vegetative activity among 

 the broad-sclerophylls and other types of plants as well. An 

 additional advantage which many of the former show at this time 

 is the possession of an increased photosynthetic apparatus, since 

 the last year's lieaves have not yet fallen and the new ones have 

 reached or are approaching maturity. It is doubtless at this period 

 that the superficial roots described on page 91 have their greatest 

 extension. A glance at figure 8 will reveal the interesting fact that it 

 was in April that the soil-moisture suffered the most rapid depletion — 

 a fact that may reasonably be referred to the abundant use of water 

 by the vegetation at this time. 



Soon after the period of maximum activity, the decreasing water- 

 supply makes a limitation of growth inevitable and necessary, and 

 it is surely more than a coincidence that a number of the species 

 drop their oldest leaves rather regularly during the month of June. 

 This phenomenon is sometimes so constant and definite that the 

 chaparral may take on a distinctly yellowish hue for a few days, 

 resuming its normal tone after the old leaves have dropped off. The 

 same is strikingly true of the broad-sclerophyll tree Arbutus, which 

 passes through a period in June when dead leaves are its most 

 conspicuous feature. It is of interest to note further that ^sculus 

 californica, not an evergreen, has a corresponding habit, dropping 

 its leaves gradually during the summer, apparently as a response to 

 the decreasing water-supply, until it is often nearly leafless before 

 autumn. After the period of leaf fall the broad-sclerophylls enter 

 a state bordering upon dormancy, growing very little, merely main- 

 taining themselves through the scanty supply of water absorbed 

 by the few roots that penetrate the deeper soil layers. 



That water lack is the reason for the stoppage of growth activity 

 is shown by the behavior of stump sprouts. If the aerial portions 

 of a shrub are removed during the dry season, even in the most 

 severe part of it, sprouts are immediately put forth which grow 

 with amazing rapidity. On Mount Tamalpais, three weeks after 

 a severe fire, I found sprouts of scrub oak 45 cm. high. Visiting the 

 scene of the Ojai Valley fire of June 1917, six weeks after the event, 

 sprouts of 90 cm. were found. In such cases the water-supply of 



