35 



number, that Malvastrtim coccineum proves poisonous to sheep which' 

 eat it. 



The question as to how long the seeds of different plants preserve 

 their vitality when buried at considerable depths in the soil is one 

 that has been much discussed but not sufficiently investigated ; and 

 facts bearing on this subject are therefore always of interest. In a 

 recent number of the Garden a correspondent gives an instance which 

 came under his notice, in which the seeds of several species of Soli- 

 dago apparently remained dormant for twenty years. The ground 

 had been covered with shrubs and carefully kept free from weeds 

 during that time ; at its expiration the ground was cleared, and two 

 years afterwards it was covered with specimens of Solidago three or 

 four feet in height. 



In an interesting paper on ''Changes in Plant Life on the San 

 Francisco Peninsula," read before the San Fr^^ncisco Academy of 

 Sciences, Feb. 2d, by Dr. Herman Behr, and published in full in the 

 Mining and Scientific Press of Feb. 21st, the author points out the 

 fact that in 1850 there were three original types of landscape which 

 could well be distinguished on the peninsula. After enumerating the 

 plants which characterized these three types, he goes on to state that 

 the latter are now no longer distinguishable, the improvements of a 

 growing city having brought them all to the same level. The original 

 arborescents have been cut down partly for fuel, and partly to make 

 room for houses. Horticulture has replaced them with the conifers 

 of the Sierras, and the evergreens of Australia, The vegetation of 

 the peninsula is at present more Australian than Californian. But it 

 is not only the quick growth of the city, the sudden change of grade, 

 etc., that have disturbed the original equilibrium in nature, for there 

 still exist places enough where an original vegetation could have re- 

 mained undisturbed, and where it was protected even against the 

 attacks of domestic animals. One of the most powerful agents in the 

 destruction of the original flora is the invasion of foreign plants. 

 Parallel with the artificial introduction of Australian arborescents 

 has come an immigration of herbaceous plants from Europe and 

 Africa, against which the native vegetation has very little power of 

 resistance. "First of all;" says Dr. Behr," I mention Silybum Mar- 

 ianum^ a native of the Mediterranean region, observed by me the first 

 time in 1854 in California, and in 1848 in South Australia. Wherever 

 it gets a hold of the soil all native vegetation disappears. California 

 is not the only land infested by this thistle. I have witnessed the 

 same invasion in Australia, and have read the statement of my former 

 teacher, Prof. Burmeister, at present in Buenos Ayres, that the same 

 thistle protects, at the time of its vegetation, the settlers against the 

 inroads of the Pampas Indians, as even the wild horsemen cannot 

 cross the immense thickets formed by this plant." Another weed, 

 Cotula coronopifolia^ does the same work in moist ground as that be- 

 gun by the Silybum in the more arid tracts of soil. This plant is a 

 native of Africa, and made its appearance in California about 1854. 

 This weed has transformed the varied aquatic vegetation of the places 

 Infested by it into one monotonous green mass with yellow buttons. 

 The graceful floating Azolla^ which formerly ornamented the creeks 



