258 REV. G. HENSLOW ON THE ORIGIN OF PLANT-STRUCTURES 
and therefore endowed with conspicuous and brightly coloured, 
often irregular corollas, honey, and other details, have to a great 
degree lost these features by a degenerating process. For if those 
structures which are correlated with insects were originally 
brought into existence by these visitors themselves, as I have 
endeavoured to prove, and if they be not “kept up” by the 
constantly applied stimulus of their visits, then the protandry, 
so general in conspicuous flowers, gives way, homogamy follows, 
and self-fertilization or autogamy is the final result, coupled 
with numerous degradations in all the floral organs. There are 
certain orders and genera which are particularly well represented 
in the Deserts, and I propose selecting a few species as being 
specialiy interesting from the peculiarities of their flowers. 
The first order to be mentioned is CrucIFER®, represented by 
over thirty species. A very common plant and one of the largest 
is the prickly bush Zilla myagroides. Another common plant is 
Diplotaxis Harra. These two agree closely in the structure of 
their flowers. The former has small, dull, brownish-pink veined 
petals ; the latter, small pale yellow flowers : in both they are about 
half an inch in length. The petals of these, as of others of the 
Crucifere and Caryophyllee, are narrow wedge-shaped or clavate 
in outline*, never having the broad limb and slender claw of 
insect-visited cruciferous flowers, such as those of the Wallflower. 
The two orifices seen from above in the last-named flower are 
closed up in these Desert plants; while the anthers closely sur- 
round the stigma, which in Diplotaxis is globular, a form which 
I have shown to be characteristic of British and other self- 
fertilizing species (e. g. Shepherd’s Purse and Pringlea antiscor- 
butica of Kerguelen’s Island). There are no honey-secreting 
glands. 
Summarizing the peculiarities of several other cruciferous 
plants, one may note that the flowers are always very small, 
the petals being narrow, often notched irregularly at the top 
(Savignya, Pl. XII. fig. 3). The colour of the corolla is often 
brownish pink above, sometimes passing into pale yellow below 
(Malcolmia egyptiaca, Zilla myagroides, Farsetia egyptiaca). 
The anthers are usually elongated, “linear-sagittate,” and always 
either just above or closely applied to the stigmas (Malcolmia 
egyptiaca, Pl. XII. fig. 4; Farsetia egyptiaca). The filaments 
may be curved inwards, bringing the anthers into close contact 
* See Pl. XII. figs. 1, 2, 3, and 8. 
