THORNS AND SPINES 



above and below. In other varieties none of the leaves 

 possess spines at all. Yet it must be admitted that these 

 are facts and cannot be denied.^ 



Moreover, the Osmanthus, with its holly-like leaves, the 

 Evergreen Oak, and some Junipers are found to show exactly 

 the same curious difference. The perilously-situated lower 

 leaves are more spiny than those which are above the reach 

 of grazing animals. 



Kerner von Marilaun^ also has remarked a similar pro- 

 tective arrangement in Gleditschia chinensis and in the Wild 

 Pear, Trees of the latter, when they are young, "bristle 

 with the spines into which the ends of the woody branches 

 are transformed"***; but tall trees twelve to fifteen feet high 

 are entirely without thorns ! 



It is when one meets coincidences of this nature that the 

 full meaning of plant life begins to dawn upon the mind. 



How is it that the plant knows the time to produce its 

 spines, and the time to refrain from doing so ? 



There are certain queer facts that have been given on 

 good authority as to the causes which tend to produce 

 thorniness and spininess. 



Linnaeus, Philos, Bot., p. 215, § 272, says: — 



"Spinosae arbores cultura saepius deponunt spinas in 

 hortis."" Lothelier found that Barberries grown in a moist 

 atmosphere had no spiny leaves, and that the thorns were far 

 less woody under those conditions, whilst in a perfectly arid 

 and dry atmosphere only spines were formed ; a strong light 

 also tended to produce spines. 



Professor Sickenberger grew a desert plant (Zilla mya- 

 groides) in the Botanic Garden at Cairo, and found that its 



^ I had expressed some doubt in my Nature Studies : Plant Life. 

 ^ Lc, vol. I, p. 433. 



i88 



