BOl'ANY. 481 



conducted a series of experiments to ascertain the relative montbly in- 

 crease in the girth of trees (Trans. Bot. Soc. Ediub., xvii), concludes 

 that in Scotland the commencement of the growing season in deciduous 

 trees is in April, and reaches its maximum in June 5 that of evergreens 

 is earlier, attaining its maximum in May. The end of the growing 

 season is for both about the end of August. The " Growth and origin 

 of multicellular plants" has been studied by Masser (Jouru. Bot. xxv). 



CHEMISTRY OF PLANTS. 



Some exceedingly interesting and valuable results have lately been 

 brought out in regard to the sources of nitrogen in plants. The long- 

 current statement that plants necessarily absorb their nitrogen in a 

 combined form seems to require moditicatiou. Indeed Lawes and Gil- 

 bert some time ago pointed out that the ordinary sources of supply in 

 the soil will account for only a fraction of the amount used by plants. 

 H. Marshall Ward (Ann. Bot. i) has given a valuable resume of "Some 

 Eeceut Publications Bearing on the Sources of Nitrogen in Plants, " 

 the first of these, the now well-known paper by Frank, published in 

 1875, aunounciug the discovery of a symbiosis between the roots of cer- 

 tain plants, notably Cupuliferic, and a fungus. These fungoid growths 

 surround the roots by a dense mycilial web. A part of the hypha? pen- 

 etrate the epidermal cells of the root, wliile the rest act as or take the 

 place of root hairs, there being in these trees no root hairs developed. 

 The fungus, it will thus be seen, is essential to the life of the host, for 

 by its aid alone is it able to take up the nutritive material of the soil. 

 Later, in 1886, Hellriegel, director of the agricultural experimental sta- 

 tion at Bernberg, iu conducting an extensive series of experiments to 

 ascertain the sources of the supply of nitrogen, reached results that 

 throw very considerable light upon the question of symbiosis as de- 

 scribed by Frank. He cultivated Gramincic in soil destitute of nitro- 

 gen and shut off from all possible sources of supply except the free air. 

 After the supply of nitrogenous materials stored up in the seed had 

 been exhausted the plants ceased to grow, and unless furnished with a 

 fresh supply, all died. Tliere can thus be no doubt that they are una- 

 ble to utilize free nitrogen from the air. On the other hand, peas cul- 

 tivated under precisely similar conditions continued to grow. The 

 only time at which the growth was stopped was when the supply in the 

 seed was exhausted, when there was a brief period of cessation of 

 growth, but this was soon overcome and the plants again became 

 healthy and vigorous. The question is, Whence came the nitrogen 

 which allowed a growth of this kind ! The only answer is that it must 

 have come from the air, and evidently the Leguminosefe possess powers 

 not enjoyed by the Gramiiia'. Uelhiegel noticed that the plants that 

 quickest recovered and were tlie most vigorous were those in which the 

 roots exhibited the largest number of the well-known tubercular swell- 

 ings, whicli, as was then known, were caused by ^vhat were called bac- 

 H. Mis. 141' 31 



