Plate li opi)osite page 149 perfectly illustrates the tempera- 

 ture effects in terms uf bud clevelo])nieiit (magnification 14 X). 

 This is a reproduction of figures 4-14 from Luyten, Toustra 

 and Blaauw (1926), and it shows the state of the growing 

 point of a tulip bulb after a four week storage at constant tem- 

 peratures ranging from 1.5° C. to 35° C. The figures show what 

 can be observed at 14 times magnification after all bulb-scales 

 and enclosing leaf bases have been removed around the grow- 

 ing point. The scars of the removed foliage leaves are indi- 

 cated and marked I. LI, LL2, etc. The main vegetative grow- 

 ing point producing the shoot for the next year is marked \'P, 

 the lateral growing point which would have developed 2 years 

 later is VPA (with its bulb scales Ri and R:;). After the 4th 

 or 5tli foliage leaf ( LL4 or LL5) was initiated, the growing 

 point widened and the petals (TI and Til), stamens (Mi and 

 Ml>) and carpels (\'D) were initiated. 



At 1.5°, 31° and 35° C. no change in the growing point had 

 taken place during the 29 days storage ; the growing points were 

 in stage I (vegetative). At 5° and 28° the 4th or 5th foliage 

 leaf had developed, and the growing point was just advanced to 

 where it changes to the flowering condition. At 9° the grow- 

 ing point was in stage III (only petals initiated), at 25.5° it 

 had reached stage VI (all flower parts, except carpels, well de- 

 veloped), and between 13° and 23" they were all in the same 

 advanced stage of development (stage VII). 



Another interesting fact can be observed as concerns the eft'ect 

 of temperature on flower initiation. When the temperature is 

 high, the normal trimerous flower is formed (23° and 25.5°), 

 but at low initiation temperatures (9°-13°) the flowers are pre- 

 dominantly tetramerous. At intermediate temperatures (17°- 

 20° ) intermediate numbers of flower parts are found. This was 

 reported in detail by Bi.aauw, Luyten and Hartsema (1932), 

 where they showed that some tulips (like "Pride of Haarlem") 

 were almost completely tetramerous at 13° C. initiation tempera- 

 ture, at which temperature the "Will. Copland" and other vari- 

 eties of tulips were trimerous. At high temperatures (28°) 

 tulip varieties initiated consistently a smaller number of flower 

 parts. 



