16 THE PLANT WORLD 



hium pusillum). Tliis mistletoe was observed on black spruce in tama- 

 rack swamps a short distance from the Michigan station. It was noticed 

 in a number of other places and seems to be widely distributed in the 

 upper peninsula, having been observed in nearly every tamarack swamp 

 to a distance of a hundred miles. Li some of the swamps nearly every 

 tree had been killed. The parasite stimulates the branches of the tree 

 to extra growth, forming witches' brooms of considerable size, and when 

 a number of branches are affected the tree dies as a result of the attack. 

 A fungus ( Wallrotliiella arceuthohn) was found parasitic in the fruit of the 

 mistletoe, and is thought that the fungus may to a considerable extent 

 check the spread of the pest. 



It has long been known that many seeds could be subjected to low 

 temperature without seriously impairing their power of germination. 

 Thus, in 1834, Edwards and Colin subjected seeds of wheat, barley, rye 

 and broad bean to a temperature which froze mercury, after which their 

 power of germination was unchanged. Wartman, in 1860, experimented 

 with a great variety of seeds, subjecting one lot to a temperature of 

 — 57°C for thirty minutes, and another to — 110°C for twenty minutes, 

 after which germination was unimpaired. A. D. Selby has recently 

 recorded [Bull. Torr. Bot. Club, 28 : 675-679] the results of some experi- 

 ments on seeds of common cultivated plants after prolonged immersion 

 in liquified air. The temperatui*e of liquified air is stated at — 190°C. 

 The seeds were immersed for i:)eriods varying from 6 to 48 hours, with 

 the result that of some, as sunflower, cucumber and rye, the germina- 

 tion was 100 per cent., of others less, but in no case were all destroyed. 

 As the author well says : " The facts lend a new significance to the latent 

 life of seeds," 



The leaves of the tulip tree, as every one knows, are among the 

 most striking of any of our native trees. They are large, glossy, green 

 leaves, rather broadly ovate in general outline, but with the upper por- 

 tion cut more or less squarely across, as though cut artificially. They 

 stand on long petioles, at the base of which is a pair of usually large 

 rounded stipules. The manner in which these stipules have originated 

 was long ago suspected from a study of certain fossil forms of Lirioden- 

 dron, but it has only recently been demonstrated by a study of the living 

 species. Edward W. Berry [see Bull. Torr. Bot. Club, 28 : 493-498] 

 has succeeded in bringing together a series of leaves which seem to 

 prove beyond question that they originated as basal lobes of the blade, 

 and have been gradually pushed down to their present position at the 

 base of the petiole. At one stage, which is well represented by a fos- 

 sil species, it was in the form of a broad margin or wing to the petiole. 



