NATURAL DISTRIBUTION OF PLANTS. 291 



family in Australia. There are no pine-trees south of the 

 equator, but an abundance of peculiar firs, with all the charac- 

 teristics of the cone-bearing family. Many species are of a 

 social nature, and occupy the ground to the exclusion of others 

 less vigorous, and these, like the Canada thistle, often become, 

 when worthless, exceedingly troublesome and injurious. Such 

 are the shrubs and coarse herbs which annoy the inhabitants of 

 the Tartarian steppes, and which encumber the soil, prevent the 

 growth of grasses, and are useful only for fuel. In like man- 

 ner, artichokes and peach-trees are said to overrun immense 

 tracts of the pampas in the Argentine Republic and the Patago- 

 nia, having been introduced from Europe and supplanted the 

 native vegetation by virtue of their superior vigor. In the 

 same way many of our most common weeds have been imported 

 from other regions, and have become naturalized so thoroughly 

 that their extermination is well-nigh impossible. The conflict 

 with evil, however, should never be remitted, notwithstanding 

 all difficulties and discouragements. It is said that over large 

 districts in the great plain of China, the most productive coun- 

 try in the world, all the native wild plants have been destroyed, 

 and only those are seen which are cultivated. It is hardly to 

 be desired that Massachusetts should be so thoroughly cultivated 

 as to destroy all the beauties of her natural vegetation ; but it 

 would be delightful to have some power capable of delivering 

 those who faithfully practise clean culture on their own premises 

 from the weeds and worms propagated upon the lands of their 

 slovenly neighbors, or of the public. 



There are two principal methods observed in nature, and 

 imitated by man, for the distribution of plants. These at first 

 seem quite dissimilar, but upon closer examination are evidently 

 alike in principle, and differ only in the degree of completeness 

 to which the natural process of reproduction is carried. Buds 

 and seeds are the essential means for the propagation of all the 

 forms of vegetation, and, therefore, especially worthy of careful 

 study with regard to their origin, nature and use. 



The simplest form of plant, such as the palmella nivalis, 

 which constitutes the red snow of arctic regions, consists of a 

 single cell with its contents. This is seen upon examination 

 under the microscope to resemble precisely an ordinary hen's 

 egg. The outer covering or shell forms a spherical cavity, and 



