30 



THE AMERICAN BOTANIST 



Germixatiox of the Cocklebur. — The fruits of the 

 common cocklebur or clotbur {Xanthiuin) have afforded the 

 scientists no end of opportunities for conjecture in regard to 

 the way the seeds germinate. In each bur there are two seeds, 

 one sHghtly higher than the other, and the botanist who orig- 

 inally tackled the problem assumed that only the lower one 

 grew the first year and thus arrived at the conclusion that this 

 was a provision of nature for accomplishing a distribution of 

 the seeds in time, by giving the species two chances for growth 

 in any region where a fruit happens to fall. Later, another 

 worker arrived at the conclusion that the delay in germination 

 of the upper seed of each fruit was due to a lack of oxygen, 

 the seed-coats being so impervious to this gas that not until 

 decay breaks through the seed coat is the plantlet within set 

 free. This has continued to be the opinion up to the present 

 time, but Prof. John H. Schaffner now reports that last sum- 

 mer, along Lake Erie, he found an abundance of sprouting 

 cocklebtirs in which both seeds had produced new plants. This 

 is rather negative evidence, to be sure, but in a measure it dis- 

 poses of the previous theories. Probably the high temperatures 

 at which the seeds grow best has as great an effect on their 

 sprouting as the lack of oxygen. 



Ferx Prothallia axd Drouth. — Although ferns are 

 supposed to be inhabitants of moist and shady places, a large 

 number grow on rocks where they are often exposed to the 

 direct rays of the sun and occasionally subjected to long periods 

 of drouth. It is something of a mystery, even to the botanist, 

 how such plants gO' so long without moisture and still survive, 

 but in most cases they manage to do it, doubtless having some- 

 thing of the vitality of the mosses, many of which are able to 

 vegetate ag^in after almost complete dessication. In the case 

 of the fern a further complication is added to the question by 

 the fact that the beginning or prothallial stage of the plant is a 

 thin green scale, one cell thick, and almost microscopic in size. 



