Dar bis hire. — Observations on Mamillaria elongata . 377 
not allow of this. For this reason I selected Mamillaria elongata as a good 
type. Of a few other Cactaceae I was able only to make a more or less 
superficial examination. The observations made on these latter, however, 
generally confirmed the opinions which I arrived at concerning Mamillaria 
elongata . 
In order to make out the structure of the plants I cut numerous 
sections, a large number of which were obtained by the aid of the 
microtome. 
The spines unfortunately cut very badly. This is not due to their 
hardness so much as to the air which they contain. All efforts to remove 
the air by an air-pump failed entirely. The resulting sections were 
generally therefore much torn, but did nevertheless help very much in 
making out the structures met with. 
The sections were stained with Kleinenberg’s haematoxylin or with 
brasilin, and mounted in Canada balsam, or they were mounted unstained 
in glycerine jelly to which some Fuchsin in a watery solution had been 
added. This last treatment gradually shows up very clearly all lignified, 
cuticularized, and suberized cell-walls which are well stained, the other 
walls being but faintly stained. 
I would like to refer here to a method I adopt for marking the glass 
slides on which microtome-sections have been mounted. The old method 
of writing on the glass with a diamond, or the not quite safe plan of 
labelling the slide, both appear to me to be too cumbrous. I now merely 
write with a pen, dipped into the white-of-egg mounting solution, on one 
end of the glass slide, which must, however, be quite clean, a few dis- 
tinguishing numbers or marks. Almost any stain will colour this albumen, 
and when dried it shows at once what the slide is. It is not easily removed 
during staining or even after. The writing can of course be replaced by 
a proper label later on when the slide is quite finished. 
B. Observations on Mamillaria elongata, P.DC. 
1. Morphology. 
Mamillaria elongata , P.DC., according to Schumann ( 26 , p. 518, 
P"ig. 83) occurs in dense clumps, and is commonly met with in the Mexican 
state of Hidalgo. It forms patches which may be 1 m. in diameter. Each 
separate upright shoot is cylindrical in form. Its height may be as much 
as 30 cm., its diameter 1-5-8 cm. The plant-body, always unbranched, is 
usually however about 7-8 cm. high (PL XXV, Fig. 1). 
As with all other species of this genus the surface of Mamillaria 
elongata is studded with numerous and very regularly arranged outgrowths 
which have been called mammae, warts, or tubercles (PI. XXV, Figs. 3, 3). 
They projec about 3-4 mm. from the main body of the plant and are 
