2 28 BOTANICAL GAZETTE [septemi^er 



rare. In the genus Viola, for example, plants with cleistogamous 

 flowers will normally produce both autosperms and xenosperms. In 

 Polygala, species exist capable, from the ecological relations of their 

 flowers, of producing a greater variety of seeds. These would differ 

 essentially in their manner of development, while resembling each 

 other structurally to such a degree that they would be indistin- 

 guishable by any of the ordinary tests. Furthermore, it may very # 

 well be that the xenosperm borne on a stock which is itself the 

 development from a xenosperm will differ intrinsically from the 

 xenosperm which is borne upon a geitonospermous or autospermous 

 stock. Thus a new element of complexity is brought in and an 

 explanation is perhaps afforded of so-called "sports" or mutations, 

 Here also may be an explanation of certain genera which include 

 large numbers of closely related "species." May it not be possible 

 that in a species there will be distinctive xenosperm, autosperm, 

 geitonosperm, and parthenosperm varieties, the continual production 

 of which gives an appearance of related species rather than of special 

 seed varieties? For example, would this explain Crataegus, Rubus, 

 and Hieracium? And may not the mutation forms of De Vries be 

 plants which have arisen from rare and unusual seed -types, developed, 

 however, in accordance with the laws of plant reproduction? 



In any event the consideration of the regular causes that underlie 

 the observed individuality of seeds may lead to useful results m 

 plant-breeding. It seems very certain that to regard seeds as 

 necessarily equivalent because borne upon the same stock is a grave 

 and positive error. They may even pass all the ordinary tests and 

 yet be extremely unlike, so much so that they will upon development 

 give rise to plants so different that they may rightly be classed as 

 different species. Returning to the analogy mentioned above, it 

 would seem as if there were no more reason to deny individuality to the 

 seeds borne in a head of grain, upon prima facie evidence, than there 

 would be to deny the individual character of each household in a city. 

 Conway MacMillan, University of Minnesota. 



THE SENSITIVE PLANT AS A WEED IN THE TROPICS. 



(with one figure) 



Everyone who has traveled much in the tropics knows that 

 Mimosa pudica is a weed which srives considerable trouble to the 



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