136 
Laboratory Note. 
LABORATORY NOTE. 
THE POLLEN OF ECHEVERIA RETUSA LINDL. AS 
LABORATORY MATERIAL. 
I N the course of experiments with the pollen of various plants 01 
the purpose of demonstrating the formation of pollen-tubes tc 
elementary classes, I have recently made use of that of Echeveria 
retusa Lindl. 
The pollen of this plant gives such exceptionally good and 
reliable results that it seems desirable to place it on record as 
useful laboratory material. 
Pollen grains germinate readily in hanging-drop preparations 
of 15% cane sugar and form tubes with unusual rapidity. For 
example, the average rate of growth of the tubes at a temperature 
of 21°C. is 540/a per hour, so that preparations suitable for class- 
demonstration purposes can be obtained without difficulty within 
an hour of transferring the pollen to sugar solution. 
To ensure satisfactory results, it is advisable to use sterile 
slides, etc., when making the drops and to transfer pollen from 
recently opened anthers. 
Pollen-tubes so obtained provide useful material for making 
direct measurements of the rate of growth of such structures and 
shew cytological features similar to those described by Strasburger 
(1) for the pollen tubes of species of Allium. 
The cytoplasm exhibits active streaming movements, and, as the 
tubes increase in length they form remarkable plug-like transverse 
septa. 
These plugs (Propfen) originate as ring-like thickenings of the 
wall, increase rapidly in thickness and quickly form a conspicuous 
pad or plug blocking the cavity of the tube. 
The substance of which the plug is composed is highly refrac¬ 
tive and gives the reactions characteristic of callose., e.g., it stains 
blue with a watery solution of aniline blue and gives a rose-red 
colour with corallin-soda. 
The pollen of several species of Sedum and of species of 
Crassula also germinates rapidly in sugar solutions of fairly high 
concentration. 
Echeveria retusa is a native of Mexico and like the majority of 
Crassulaceous species is a leaf-succulent with rosette habit. 
Rapid germination of the pollen and a preference for solutions 
of relatively high osmotic pressure may well be biological features in 
these plants associated with the xerophytic conditions under which 
they occur in nature. 
It would be of interest to know whether the pollen of other 
groups of succulents, e.g., Cactacea 2 , exhibits similar tendencies. 
M. C. Rayner. 
Botanical Laboratory, 
University College, 
Reading. 
LITERATURE. 
1. Strasburger, E. Das botanische PraktiUum, 1902, p. 537. 
