THE AMERICAN BOTANIST ' 55 



The Radial Type in Plants. — One interestine: differ- 

 ence between the higher animals and plants that was long ago 

 pointed out is that the animals have a fore-and-aft polarity 

 while the plants are up an'd down structures. Still another 

 feature of plants dwelt upon by L. H. Bailey in his "Survival 

 of the Unlike" is the circular form that all vegetation tends to 

 take while animals are nearly all bilateral or two-sided. The 

 tendency to spread out in all directions is very strong in plants. 

 Tree trunks are round and branches are given off on all sides ; 

 the leaves, parts of the flower and even the seeds in the fruit are 

 for the most part arranged in circular fonn while in the high- 

 est type of plants, the asters and other composites, the flowers 

 themselves are arranged in this fashion. So characteristic is 

 the rotate form that any deviation from it is at once marked 

 as a specialization and we commonly hold the flowers of 

 orchids and labiates more highly specialized than those with 

 parts regularly arranged. 



Crop and Weed. — It has come to be recognized th. t 

 there are natural associations of plants and natural rotations 

 of vegetation certainly determined by other than pla.it j'ood 

 factors. Thus in the Eastern United States, whea*: is foil ) /ed 

 by ragweed naturally while, across the fence, cockelbur and 

 wild sunflowers come in after the corn, the difference 'n ege- 

 tation being as sharply marked after the removal of the crops 

 as when they still occupied the land. Analyses of th.e ragweed, 

 for instance, although it is a shallow^er rooted crop than wheat, 

 show that it takes from the soil as much of the mineral nu- 

 trients as does the preceding wheat crop. The investigation of 

 Lawes and Gilbert on fairy rings can not be satisfactorily ex- 

 plained by the comparison of the mineral constituents of the 

 soil within and without the rings. Work at Woodbiirn on rhe 

 effect of grass on apple trees finds no other phusible explana- 

 tion than that the growing grass produces in the soil organic 

 substances detrimental to young apple trees. — Science. 



