147 



the actual forms of witches-broom, the tendency at present is to place under 

 this head of bud variation the numerous spherical bushes of the spruce 

 witches-broom^. The greatest number of examples is furnished by the 

 many cultivated plants of our gardens in the so-called globe forms of coni- 

 fers and in the dwarf forms of blossoming bushes. In the short-lived sum- 

 mer plants (Ageratum. Zinnia, Tagetes, etc.) we find that the dwarf growth 

 can become an hereditary peculiarity, persistent in the seed. 



Too Thick Seeding. 



A limitation of the soil space and a struggle for water and nutritive 

 substances is always produced by too thick seeding. The struggle of the 

 plants with one another for their food appears earliest and sharpest in sandy 

 soils. Besides the dwarfing of individual specimens, the weakening of repro- 

 duction deserves especial consideration. This becomes evident not only in 

 the decrease of the blossoms, but also in the change in their character and 

 becomes especially perceptible in horticulture, because staminate blossoms 

 are produced predominantly. The unavoidable scarcity of nitrogen is also 

 a factor. The greater the amount of nitrogen supplied, the more abundant 

 the meristem, rich in cytoplasm. 



Hoffmann- gives the results of many cultural experiments in pots and 

 open ground, to determine the influence of too thick seeding for different 

 plants. In this, for every loo pistillate blossoms there developed the follow- 

 ing number of staminate ones : — 



With a more seat- 

 In With Too Thick Seeding, tered position of 



the plants. 



Lychnis diiirna 233 125 



200 yy 



" vespertina 150 73 



Mercurialis annua 100 90 



Rumex Acetosella 152 81 



Spinacia oleracea (average of 



several sowings) 283 y6 



In Cannabis his results were contradictory, which may be explained by 

 a consideration of Fisch's statement^' that the proportion of the sexes in 

 hemp is already determined in the seed, — that, therefore, external in- 

 fluences can bring about no further changes. Belhomme maintains that the 

 form of the hemp seeds admits of conclusions as to the sex of the future 

 plant, since the longer or the more spherical form, as in bird's eggs, indicates 

 a staminate or a pistillate individual. 



Since the phenomena appearing with too thick seeding may be traced 

 essentially to scarcity of food substances, further examples will be cited 

 when the scarcity of nitrogen is discussed. 



1 Tubeuf and Schroter, Naturwissensch. Zeit-schr. f. Land- 11 Forstwirtschaft. 

 1905, p. 254. 



2 Hoffmann, H., Ueber Sexualitat. Bot. Zeituns'. 18S5. No. 16. 



3 Fisch, Ber. der Deutsch. Bot. Gesellsch. 1887. Vol. 5. Part 3. 



