Chapter VII —109— Artificial Factors 



Lastly, in the fourth group we placed those species that showed normal 

 vegetative growth but that, due to lack of the proper conditions for 

 their normal development, did not flower at all or, if they flowered, 

 did not form any fruits or formed fruits without seeds or with inviable 

 seeds. (Examples: Pinus Gerardiana, Pseudotsiiga taxifolia, Clematis 

 Jacqmannii, Pueraria Thunhergiana). 



According to Chernova (1939), out of a total of 681 woody, orna- 

 mental species now grown in the Nikita Botanical Gardens only 40 are 

 self-propagating. Most of the others (381) produce viable seed but 

 are not self -propagating, 81 do not produce viable seed, 76 bear fruit 

 but produce no seed, and 103 flower but do not fruit. It is, thus, clear 

 that a plant, even when transferred to a region with similar habitat 

 conditions, has serious obstacles to overcome before it can become 

 fully naturalized. This accounts for the very small percentage of 

 species that actuaOy enter into the composition of the wild flora of a 

 country, not merely here and there crossing the boundaries of botanical 

 gardens or plantations but actually extending their range outside these 

 boundaries. Despite the centuries-long work of botanical gardens and 

 accHmatization nurseries, involving the introduction into cultivation of 

 tens of thousands of species, most of these species, though continuing 

 to this day to grow in these gardens and nurseries under man's pro- 

 tection and with his care, have not in the slightest been able to emanci- 

 pate themselves from this dependence. Any number of examples 

 might be cited to illustrate this. Thus, though thousands of species of 

 woody and herbaceous plants have been introduced at the Nikita 

 Botanical Gardens, only about 700, aknost exclusively woody species, 

 have been preserved to the present day. The records show that there 

 existed at these Gardens considerable collections, several times re- 

 plenished, of herbaceous plants, but of these not a trace has been pre- 

 served. 



Stankov (1925) made a count of the species in southern Crimea 

 that had spread beyond the limits of the parks, where they had at one 

 time been grown, and had become wild. Of such species he found that 

 he could list with certainty only 19. Moreover, the habitats of these 

 plants, with very few exceptions, were found to be near the places 

 where they had once been cultivated. These plants are not widely 

 distributed, and it is evident, beyond any doubt, that they are escapes 

 from cultivation. 



Though cases are not rare of accidentally or intentionally introduced 

 species spreading very rapidly and, on territory where the native vege- 

 tation has been disturbed or destroyed, acquiring a dominant position, 

 it usually happens that such species later as suddenly disappear as 

 they had appeared. Thus, Flahault (1899) describes how in 1856 

 there were listed at the Montpellier Botanical Gardens 24 naturalized 

 species, all of which later ceased to propagate themselves independently. 

 In 1893 in the same gardens there were 57 flowering species alien to the 

 local flora distributed throughout the territory of the gardens and con- 

 stituting noxious weeds that had to be controlled. Six years later, in 

 1899, seven of these species had completely disappeared, and four had 

 ceased to be universally distributed. Taking their place, nine new 

 species had made their appearance. But not one of these plants ever 

 spread beyond the boundaries of the gardens. 



