( 170 ) 



During the first weeks generally no striking changes are observed 

 until after about a month a varying number of local elevations, 

 yellow like the leaf-tip that produces them, becomes prominent and 

 reveals the differentiation of special proliferating centres. 



As a rule we see these grow to real knobs, especially in the 

 direction perpendicular to the surface of the leaf. 



While the knobs are still relatively small, brownish grey streaks 

 begin to appear on their tops, which gradually extend, so that 

 finally the whole knobbed surface becomes brown. 



For some time such a knob shows nothing particular, except that 

 it becomes larger and thicker. Next on a certain day a small opening 

 is formed in its top, through which a small green point projects, 

 which will grow out into a leafed sprout. 



As well on the lower as on the upper surface of the leaf-tip 

 knobs may form. Mostly they form on the upper surface, though. 

 With some leaves I have observed knobs on both sides at the 

 same time. 



The observations on the time, needed by a leaf in order to form 

 "ripe" knobs, after the yellow vesicles have appeared, have led to 

 somewhat diverging results. The shortest period was observed with 

 leaves on the upper branches or in the periphery of the crown, 

 which consequently occupied the most favourable position with regard 

 to light. On these good-sized, brown knobs had generally formed 

 half a year after the appearance of the yellow vesicles. 



Also for the question, how old and how large a knob must be in 

 order to open and give the adventitious bud an opportunity for 

 sprouting, no rule can be fixed. I saw one sprout five weeks after 

 the knob had first been observed as a special elevation, while others 

 were still closed after five to seven months. 



About the size of the knobs we may state that some knobs, 

 scarcely rising more than a millimetre above the surface of the 

 leaf-tip, opened, while others of double and even treble the height 

 remained obstinately closed. Yet these latter contain as well an 

 adventitious bud and not seldom even more than one. 



The microscopical investigation was for the greater part carried 

 out on microtome preparations. For fixing the material 1 used the 

 mixture: zincchloride-glacial acetic acid-alcohol, (2 grains of zinc- 

 chloride and 2 ccm. of glacial acetic acid to 100 ccm. of alcohol of 

 45—50 put), recommended by Juel '). The particular hardness of 



»j H 0. Juel, Ueber den Pollenschlauch von Cupressiis. 'Flora. Bd. 93. 1904. 

 pag. 56—621. 



