Significance of Spines in Discaria Toumatou. 81 
comparison in the soil of the pot a spiny adult shoot taken from a 
plant on a sand-hill near by. As no changes of any moment have 
taken place in the plants since the photograph was taken beyond 
increase in size and number of shoots, it suffices to show clearly 
the striking difference that exists in appearance between juveniles 
and adults, so that no detailed description of the two forms is 
necessary. 1 Here it need only be pointed out that the moist-air 
leaves are smaller and considerably thinner than those of the adult, 
and that, like those of the normal plant, they were cast off each 
year in the autumn. The twigs have a drooping habit, but some¬ 
times arch upwards at their extremities, a light-relation due to 
unequal illumination, as is also the more or less distichous arrange¬ 
ment of the leaves. 
After being placed in the moist chamber, the plants developed 
no more spines and are now seedling plants in all respects except 
for the few spines, which were developed prior to the culture in 
moist air. Moreover it seems evident that such plants would 
remain in the seedling form so long as they were kept in an 
atmosphere constantly moist and exposed to a feeble light. Even 
an adult shoot on a full grown plant in the open and freely 
producing spines, may have any further production of such 
suppressed at once, if the shoot should continue its growth under 
slightly more hygrophytic conditions. Thus quite recently, I 
observed on the clay hills near Wellington, a shoot creeping near 
the ground whose apical portion was covered by grass. This shoot 
where fully exposed to the light was spinous as usual, but where 
shaded and in a slightly moister atmosphere was quite without 
spines. 
From the above it follows that the production of spines in 
Discaria Toumaiou can be controlled at will by specifically changing 
its environment—a plant exposed to a dry atmosphere and normal 
light producing spines, whilst one exposed to a moist atmosphere 
and a feeble light produces no spines, but in their place leafy shoots 
of unlimited growth. 
That spines on xerophytic plants are an adaptation against the 
attacks of grazing animals is a matter of such general belief as to 
be admitted into certain botanical text books as a proved fact. 2 
1 The result of this experiment is briefly mentioned in a paper 
read by me at the Dunedin meeting of Austral.' Assoc, for 
Adv. of Sc. and published in Journ. Agric. and Past. Assoc. 
Canty-, Jan. 1904. 
2 e.g. Strasburger’s Text Book of Botany, 1903., p. 27. (Eng. 
Trans). 
