4 Wisconsin Academy of Sciences, Arts, and Letters. 



trees Spath 7 comes to still another conclusion. According to 

 him the occurrence of the June elongation-growth which makes 

 its appearance fairly regularly on vigorous young trees of oak and 

 beech, is not determined by the environment but follows the 

 close of the spring elongation period after a fairly definite in- 

 terval of time, and may even develo pduring a drought or while 

 conditions are extremely unfavorable for growth. In Quercus 

 the resting period between the spring and June growth was 

 from 30 to 40 days and in Fagus from 15 to 20 days. It is said 

 to last 9 to 16 days in the former and 13 to 24 days in the lat- 

 ter. The length of these second shoots is thought to depend 

 chiefly upon the amount of available water and is usually but 

 not always less than that of spring shoots. The species with the 

 June-elongation habit have a short but very active spring- 

 growth period as compared with those not having the June 

 growth. It was found impossible to prevent the June elonga- 

 tion growth by reducing the food and water supply and by low- 

 ering the temperature, nor could it be made to continue beyond 

 the ordinary period by supplying heat, moisture and food con- 

 ditions favorable for growth. 



Spath also found that the second growth is made up of three 

 types. In one kind the axillary buds of an elongating shoot devel- 

 op into branches before they are fully formed. This happens in 

 Salix, Populus, Taxus, Buxus, Prunus, Pyrus, and is called syllep- 

 tic growth. In the second type known as June growth ( Johannes- 

 trieb) the buds are fully formed before they open after the ter- 

 mination of the spring elongation growth. The third type is 

 called proleptic growth and is said to develop at any time during 

 summer from buds which normally would not have opened until 

 the following spring but which open early owing to wound or 

 some other strong environmental stimulus. 



Neither sylleptic nor June elongation-growth was said to have 

 a zonation effect upon radial growth while the production of 

 proleptic shoots practically always resulted in more or less dis- 

 tinct zonation of the radial growth. This was shown during 

 their development by the wood cells produced being wider than 

 those differentiated just before the new shoots appeared. 



7 Spath, H. L. Der Johannistrieb. Ein Beitrag zur Kenntniss der 

 Feriodizitat imd Jahresringbildung sommergruner Holzgewa.ch.se. Ber- 

 lin, 1912. pp. 91. 



