January 25, 1895.] 



SCIENCE. 



98 



tinental area.* A floral caloiular might be 

 constructed with the dates of germination, 

 seed discharge and death of annual plants, 

 and it would be found that a plant year 

 after year departs very little in the time of its 

 appearance from the dates put down in this 

 vegetal almanac. Take a common agricul- 

 tural plant by way of illustration. The 

 planting season for Indian corn is ft-om the 

 1st to the 10th of ^May in favorable weather. 

 One hundred and ten days from date of 

 sprouting to date of ripening or security from 

 frost is about the average season. In many 

 cases in the corn belt, Nebraska for instance, 

 the farmers are quite sure of at least one 

 luindred and twenty days. All this goes to 

 prove that each plant has a peculiarity of 

 its o\^^l with regard to temperature and en- 

 vironment; that the sum of the mean daily 

 temperatures from the time of sprouting un- 

 til the time of seed discharge is pretty nearly 

 a constant one, and that if a plant be 

 watched for years in succession it will be 

 found that this thermometric sum oscillates 

 little either way from the plant's normal. 

 It is desiral)le that our native plants should 

 be investigated as to temperature condi- 

 tions, for some rule must determine the 

 appearance of plants, the time of flowering 

 and the time of suspended growth. It is 

 no liaphazard process, but depends on 

 fixed laws of growth and development. 

 The daily appearance of new plants de- 

 pends considerably more on the habits of 

 their ancestors than on the controlling 

 influence of present meteorological condi- 

 ticms. 



Our forest trees show some very interest- 

 ing peculiarities in their early spring devel- 

 opment, which is apj>arently caused liy tlieir 

 past conditions of growth and development. 

 Heredity seems to i>lay a very important 

 role in their vegetative habits. The facts 

 condensed in the accompanying taltle will 

 help to elucidate this statement : 



*Sec HarjM'r'.'t Jfarjtniiic, May, 1894. 



Plants 

 wind- 

 fertilized, 

 flowerinf^ 

 from 

 March 



to 

 June. 



Cretaoeons 

 or Chalk 

 Pcriotl. 



Post- 

 Cietaoeous 



Querc-u.s (oiiks), Fajjus 

 (Iwcfhcs), .Siilix (wil- 

 lows), Platanus (plane- 

 trees), SiLssiifras, IjiuniK, 



J Magnolia, Lirioilenilrou, 

 (tulip-trees), Mvrica 

 (wax myrtles), Betula 

 (birches), Liqnidambar 

 (gum-trees), .Fuglans 



I. (walnuts), .\cer(maples). 



Conius (dog- wood), 

 Xyssa ( sour-gums ), Frax- 

 inus (a.shes). 



Ulmiis ( elms ), planera, 

 Celtis, Carya (hickory), 

 I accmiKin (hlue-berries). 



Almus (alders), Car- 

 Miocene. ^ pinus (horn-beam), Xe- 

 gundo. 

 Italicized genera insect-fertilized. 



It will be seen from this table that the 

 more important genei-a of trees flower in the 

 early spring. The cause for this is to be 

 found in the past history of the plants, for 

 if we arrange them, as in the table, as to 

 their appearance in geological time, we dis- 

 cover that nearly all of them appeared be- 

 fore or during the Miocene (middle Tertiary 

 or Mammalian Age) Epoch, wlien the north- 

 ern hemisphere was many degi-ees warmer 

 than at present, and when a mild climate 

 extended far into the arctic regions. It is 

 impossible to ignore the force of the testi- 

 mony as to the continuous warm climate 

 of the north temperate and polar zones 

 throughout Tertiary (Mammalian) Times. 

 We have in the lower Cretaceous (Chalk) 

 Period an almost tropical climate down to 

 the upper Eocene (Lower Tertiary), when 

 it remains warm temperate, for instance, 

 in central Europe and cold temperate 

 within the polar area. It then gradually 

 cools down and merges through the Pliocene 

 (tapper Mammalian ) into the Glacial Epoch. 

 That being the case, it is highly probable 

 that the .season of growth of our forest ti-ees 

 during the Miocene Period was uninter- 

 rupted, and that flowers followed rapid vege- 

 tation, as night follows daj-. The Glacial 

 Period succeeded with its cold acting as a 



