148 YEARBOOK, PUBLIC MUSEUM, MILWAUKEE [Vol. Ill, 



differences in soil, temperature, light intensity and moisture. In the 

 rose family, hybridization is the chief cause of variation. In certain 

 species of blackberries, the intensity of the light has a strong influence 

 on the prickles. The fertility of the soil influences the size of the plant, 

 especially the size of the leaves. 



The following genera belonging to the Rose family are found in 

 Wisconsin: ninebark (Physocarpus) , spiraea (Spiraea), apple (Pyrus), 

 plum (Prunus), juneberry (Amelanchier) , hawthorn (Crataegus), 

 strawberry (Fragaria), barren strawberry (Waldsteinia), cinquefoil 

 (Potentilla) , avens (Geuni), blackberry and raspberry {Ruhus) and 

 the rose (Rosa). Here only the variable genera will be discussed, as 

 the other genera are fairly constant and easy to determine. The 

 variable genera include some of our most important economic plants, 

 a rather detailed description of which is not amiss. 



Five species of blackberries occur in the state and most of them are 

 widely distributed. Like many other of our plants, we do not ap- 

 preciate them. We spend fortunes to import foreign plants not nearly 

 as desirable as our own. Nature does not produce a more luscious 

 and healthful fruit than the blackberry. 



The blackberries are sinners when it comes to the art of deviating 

 from rules and regulations. Different species grow side by side. A 

 bumblebee comes along and carries the pollen from one to another 

 and the crime is committed. Some of the resulting plants will re- 

 semble the mother; others the father, while some will be a mixture of 

 both of the parents. Many a botanist has roundh' cursed this group, 

 while others have rejoiced because of the chance to make species to 

 one's heart's content. Thirty years ago all of the blackberries occur- 

 ring in northeastern America could be confined to less than ten species. 

 Gray's Manual, 7th Edition lists thirty-eight for the northeastern 

 United States. In England over one hundred species have been rec- 

 ognized. Ezra Brainerd, for years president of Middlebury College, 

 made a careful study of the group. He recognized that many of the 

 so-called species were hybrids. With the assistance of A. K. Peiter- 

 sen of the Vermont Experiment Station, a large number of the wild 

 species were transplanted to a control garden and artificial crosses 

 were made the offspring being carefully observed for several genera- 

 tions.'' Their results gave evidence that of the large number of species 

 listed for New England, only twelve were valid. Many of the other 

 forms they actually produced by crossing. 



siBrainerd & Peitersen, "Blackberries of New England — Their Classification" — Bulletin 217, 

 Vernjont Agricultural Experiment Station. 



