STATISTICS OF METASPERMAE. 723 



dones are preponderant and the Archichlamydeae intermediate. 

 In both the SE. and SW. elements the Metachlamydeae are 

 preponderant and the Archichlamydeae intermediate. These 

 facts are seen to be exactly in line with the rest that have been 

 given. In the NW. element which is numerically the smallest 

 of all the combination elements, the Archichlamydeae are pre- 

 ponderant while the Monocotyledones and Metachlamydeae; 

 for their respective numbers, contribute about equally to the 

 element. This is probably to be attributed to two facts. 

 First, the Siberian and the N. W. T. influence would be felt 

 most strongly in the NW. element and this influence would 

 consist principally of monocotyledonous and archichlamydeous 

 forms. Second, the Monocotyledones of this influence would 

 be generally more widely distributed in North America than 

 the Archichlamydeae, so that they would be probably entered 

 either in the NEW. or NSEW. elements. The Metach- 

 lamydeae then through their endemic and north-bound char- 

 acteristics and the Monocotyledones through their general and 

 south or north-bound characteristics have either failed, on the 

 one hand to make the N. W. range or, on the other have ranged 

 beyond and are in the more general categories. The inter- 

 mediate condition of the Archichlamydeae is then, after all, 

 the cause of their preponderance in the NW. element. Ap- 

 parently, too, if the existence of the diagonal tension, dis- 

 cussed above, were borne out by further examination it would 

 be possible for such a condition to appear in no other ele- 

 ment than the NW. For in the NE. the Monocotyledones 

 would have their greater ease of distribution to increase their 

 preponderance while in the SE. and SW. the Metachlamy- 

 deae would in varying ratios predominate. 



In general, then, the combination elements serve to add to 

 the weight of evidence in favor of considering the Metachlamy- 

 deae, Archichlamydeae and Monocotyledones of different and 

 more or less definite meaning as components. The two special 

 cases are the NSW. and the NW. and an attempt, probably 

 imperfect although, it is hoped, suggestive, has been made 

 to show how in their case special topographical or geographical 

 conditions have served to modify the more general biological 

 conditions. 



Of the 1.174 species and varieties considered as indigenous 

 to the Minnesota valley, 3 17 are of extracontinental range. 

 This number is quite exclusive of the 130 species and varieties 

 which have been introduced into the Minnesota valley during 



