38 The Irish Naturalist. February, 



on one side of it. Against the inexorable line there is no 

 appeal. Be there a thousand plants of a species on the one 

 hand, they are of no avail if there be one on the other. What 

 are we to say of a list of " Western Plants " of Ireland {Cybele, 

 p. Iv.) in which Saxifraga twibrosdy Euphorbia hiberna^ 

 Tricho7?ianes radicals, find no place ? 



My " types" have been formed according to a quite different 

 principle. The distribution of species is infinitely varied. If 

 we have 1,200 flowering plants in Ireland, then there are just 

 1,200 types of distribution. Mapped, the lines defining their 

 range of occurrence and of frequency would appear as a 

 complicated series of curves intersecting in every direction. 

 The task to which I devoted .six months, with what little 

 success others must judge, was to discover by means of a 

 study of the mapped range of each member of our flora the 

 lines along which the most marked coincidences of such 

 curves were to be found. These are the true phytological 

 boundaries. The various ''strong lines" thus appearing, had 

 finally to be grouped into one or two simple curves, to 

 represent the dominant floral boundary lines. Needless to 

 say, these lines do not fit in with any parallels of latitude, or 

 political provinces, or other artificial boundaries ; but by an 

 allowable generalization they may be shown as one or two 

 simple and easily remembered lines or curves. Thus, instead 

 of making the plants fit a prescribed boundary, it has been 

 my aim to make the boundary fit the plants. 



The same synthetic process may lead to a wide over- 

 lap between species of different types — another point of 

 which Mr. Colgan falls foul. I may observe in passing 

 that in the general conception of natural plant-groups, 

 their boundaries, and overlaps, I have, as I stated in my 

 paper, endeavoured to follo^v in the footsteps of our greatest 

 botanical geographer, Hewett Cottrell Watson. Watson, 

 indeed, omits (perhaps wisely) to lay down any bounding 

 limit whatever for his British types ; " Plants chiefly seen 

 in West England" is a far vaguer type definition than mine, 

 which my reviewer thinks are not definite enough. Then, as 

 to overlap, we may find plants of Watson's English tj^pe far 

 up in the Highlands, and "Scottish" plants on the shores of 

 the English Channel. " Atlantic " .species occur on the east 



