THE GENUS CRATAEGUS IN NORTH AMERICA 



291 



small area, while individuals of allied species may frequently occur 

 within a few feet of one another. 



While Crataegus is certainly common in eastern North America, 

 its distribution is by no means general. Colonies occur, as at 

 Buffalo and Niagara Falls in New York, where in areas of a few 

 acres fifteen or twenty distinct forms, belonging perhaps to four or 

 five of the primary groups, grow together with many individuals, 

 while outside of such great colonies it is often difficult to find a 

 single plant over large adjacent regions. It is probable that the 

 plants have largely increased in numbers since the general settle- 

 ment and clearing of the country, for Cratagus is not a true forest 

 plant and thrives and spreads only in open situations. That they 

 are not more abundant and more generally distributed, and that the 

 large colonies are frequently found on the waste ground in the 

 neighbourhood of towns is due, no doubt, to the fact that farmers, 

 especially in the northern States and Canada, consider the presence 

 of thorns on their land as indicative of bad farming and cut them 

 down as fast as they appear. 



The study of the genus presents many difficulties. Herbarium 

 specimens, unless they can be made in both spring and autumn 

 from the same plant, and unless they are accompanied with accu- 

 rate notes on the colour of the anthers, have no practical value. 

 Many of the species look so different in the spring and in the 

 autumn that it is essential to number carefully each plant from 

 which specimens are taken. Collectors willing to undertake such 

 troublesome work are not to be found in much of the vast region 

 over which Cratmjus is scattered ; and the blooming period of the 

 different forms which may occur in any given region may extend 

 through several weeks, and as each species remains in flower for 

 only a few days, such a region must be visited several times in 

 order to secure the flowers of all the forms ; while in the autumn 

 the ripening of the fruit in any given locality may extend from 

 August to November. Many visits have to be made, therefore, to 

 a station before sufficient material for the description of all the 

 forms which mav occur there can be obtained, and the number of 

 such stations that one observer can visit satisfactorily in one season 

 is necessarily small. The difficulties are increased, moreqver, by 

 the fact that Cratagus does not flower every year, and that the fruit 

 is sometimes destroyed by insects or disease. Much work has 

 already been accomplished, but much more remains to be done. 

 The plants growing in only a few small regions have been critically 

 studied, and there are still thousands of square miles in the United 

 States and Canada where Cratagus is known to exist, and where no 

 systematic collections have been made. In every township of half 

 a dozen States it is more than probable that forms exist which 

 differ from those that have already been described, and many years 

 will be needed to elucidate the characters and distribution of the 



genus in this country. 



The investigation at best can only be carried on slowly and with 

 full knowledge of all the characters of each plant described. The 

 importance of deliberation has already been shown, and the diffi- 



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