journal

20 THE CACTUS AND SUCCULENT January, 1951
SPINES
By S. NAYLOR
There is, in the majority of people, an innate desire to know the how and why of the things we are interested in.
This urge is strongly present when contemplating the cactus on our greenhouse staging. The feature which
has intrigued me of late is the spine or prickle (the latter being the word preferred by the botanist) in its many
forms, colouration and orderly arrangement.
Query after query present themselves to one's mind, such as, how are they produced and of what are they
composed, when did they first appear, and what purpose or purposes do they serve ; where can one find the
answer, or, at least, a reasonable explanation ? These and many more are the perplexities one has constantly
before the mind.
The growning glory of all vegetation is, undoubtedly, its flora, and the cactus is not behind any of them for
beauty, but this beauty is fleeting and fades unseen by mortal eye in most cases. However, the resultant seed
affects the perpetuation of its genera and the purpose is served.
The Cactus Family has yet another glory not shared by any other botanical group, in which it is quite unique,
namely, the production of spines, also of their nature and the orderly arrangement of them and in their presence
on almost every species of the family.
As with the flora, there is here, in the spine, also a beauty of colour and form, but, additionally, a symmetric
pattern which holds the eye by reason of its outstanding effect. This order or precision of spine arrangement is
produced by the even spacing on a spiral round the body of the area we designate as the areole (the root meaning
is area).
In some species, there is a single spiral and in others a number, progressing upwards together, or side by side.
Compare the Pereskia, or one of the cylindrical Opuntias, with an Ech/nopsis, viewed from above, when the spirals can
be best seen and counted.
Spines only occur at the areole and in that area have a centre of growth of their own, as is demonstrated
in the case of the Coryphanthanae. In this genera the flower appears in the axils of the tubercle, while the spines
are at the tip or outer extremity, showing a division of two centres of production. With all other species, as far
as I have been able to obssrve, the flower develops immediately above the spine cluster, as do also the offsets,
so evident in some of the species. One peculiar aberration, recently noticed, was the development of an offset
instead of a seed berry, with the tube of the flower encasing it. This was on a Mammillaria gracilis. The wool or
hair, which adorns so many species at the areole, appear to serve the good purpose of protecting the flower and
subsequent seed producing area, from knocks or sun scorching.
The spine is a most remarkable production in that it is composed, in the main, of a form of silica and does not,
when mature, contain any living cells, which fact accounts for its stiff, rigid toughness. Presumably these cells,
having produced the spine, cease to live because their work is complete. Silica is a non-metallic element, very
much like carbon and is very abundant in nature. Flint is one kind frequently seen. Silica is commonly present
in varied rock formations and, mixed with their oxides, throughout the earth. As a result of this wide distribution
in the soil, very minute particles are present in ground water and are absorbed, being found in large proportion in
the flesh of the cactus.
This otherwise useless constituent is employed to make the vulnerable spine and protective hair. This brings
us, naturally, to a consideration of the obvious usefulness of the spine as a protective agent from grazing animals
and of man, until he found the easy way of ridding himself of them by burning. They serve the useful purpose
of providing shade from scorching sun and also act as a brake to searing wind. Possibly they also assist in the
supply of water to the roots by conducting atmospheric moisture and naturally draining it downwards.
Another self-evident use of the spine is presented in the remarkable barbed v/eapon of the Opuntiae. Having
caught the fur or entered the flesh of an animal, the pad or broken branch is carried away for some distance before
the tortured animal removes it by one means or another. There to lie and eventually root itself, so forming another
colony. These remarks apply also to the hooked type of spine seen on some Mammillarias.
Of the foregoing, that which is conjecture justifies itself, it seems to me, until some authority or authorities
come to our rescue by producing an " a posteriori " such as we are looking for, which will satisfy our desires and
add to the recorded knowledge of our subject.