96 



SCIENCE. 



[N. S. Vol. I. No. 4. 



period of some months that growth com- 

 mences anew, and this fi-equently under 

 circumstances which appear far less favor- 

 able — especially at a conspicuously lower 

 temperature. "This periodic alternation 

 of vegetative activitj^ and i-est is in general 

 so regulated that, for a given species of plant, 

 both occiTr at definite times of the year, 

 leading to the iaference that the periodicity 

 only depends upon the alternation of the 

 seasons, and therefore chiefly upon that of 

 temperature and moisture." A few well- 

 known examples are selected for illustration. 

 ' ' The leaf-shoot and flowers contained in 

 the bulb of the Crown Imperial commence 

 to grow vigorouslj' in the spring-time with 

 us, even at the beginning or middle of 

 March, when the soil in which the bulb has 

 passed the winter possesses a temperature 

 of 6-10° C; the leaf-shoots protrude for- 

 cibly from the cold earth to grow vigor- 

 ously in the but slightly warmer air. There 

 would be but little to surprise us in this, if 

 we did not at the same time notice the fact 

 that a new leaf-shoot is alreadj' formed in 

 embrj'o in the subterranean bulb in AprU 

 and May; this shoot, however, does not grow 

 to any extent in the warm soil during the 

 summer and autumn. On the contrary, 

 this favorable period of vegetation passes by, 

 until at the end of the winter an iuconsider- 

 able I'ise of temperature above the freezuig 

 point suffices to mduce vigorous growth ; and 

 as is well known, the same is the case with 

 most bulbous and tuberous plants, as the 

 meadow saffron, potato and kitchen onion." 

 " I have man jr times attempted to induce 

 the tubers and bulbs ripened in autumn to 

 put forth their germinal shoots during N'o- 

 vember, December and January, bj^ laying 

 them in moist, warm loose soil ; but as in 

 the case of the potato, as well as in that of 

 the kitchen onion, no trace of germination 

 appeared. If, on the other hand, the at- 

 tempt is repeated in February, or still better 

 in March, the germhial buds begin to grow 



vigorouslj' even in a few days. It is evident 

 that some internal change must have taken 

 place in the tubers and bulbs during the 

 winter months, when it is impossible to bring 

 them into activity fi-om their state of rest." 

 Our spring plants in this agree physiologic- 

 ally with their arctic congeners. The period 

 of rest described above in such early spring 

 plants, as the winter aconite, crocus, Ery- 

 thronium, etc., has ia my opinion been due 

 to the influence of the glacial cold heredit- 

 arily impressed on these plants in con- 

 nection mth the chemical changes which go 

 on. The following diagrams will illustrate 

 my meaning. Diagram B shows that the 

 period of vegetative activity of our sprmg 

 plants corresponds with an arctic or a glacial 

 summer, while the dormant period corre- 

 sponds with an arctic winter, although our 

 present summer has encroached on the 

 former glacial winter. 



Astronomical Year, Glacial Period. 



Present Summer. Present Winter. 



It was necessary for this rapid gro'wiih 

 that the food material should be prepared be- 

 forehand, because the arctic or glacial sum- 

 mer is an exceedingly short one. Mr. Henry 

 Seebohm,* in his presidential address before 

 the Geographical Section of the British As- 

 sociation, gave a gi-aphic description of the 

 succession of the seasons in high arctic lati- 

 tudes. A few sentences are worth quoting 

 in this connection. He said that the stealthy 

 approach of winter on the confines of the 

 polar basin is in strong contrast to the 



*See Pojmlar Science Monihhj, XLV., 138, May, 1894. 



