OF TIGRIDIA. Se 
the embryo-sac. I propose to describe the pollen-tube in 
various parts of its course, to state the results of experiments 
performed by Dr. Maclean* and myself, upon the indepen- 
dence of the tube of the pollen-grain after it has once passed 
into the style, and to explain the change which occurs in the 
tube at its contact with the embryo-sac. 
The pollen-grain of Tigridia is large, oval, and contains in 
its external coat much oil; it is barely visible to the naked 
eye, yet it is the originator of a tube which passes along at 
least four inches of stigma, style and axis, in less than twenty- 
four hours ; this tube perforates the stigma, insinuates itself 
between the cells of this organ, and reaches the so-called con- 
ducting tissue of the style. This tissue ought, for reasons 
presently to be given, to be called nourishing tissue. 
The fact is that the life of the pollen-tube is very short, and 
the period which elapses between the application of the pollen- 
grain and the entrance of the tube into the ovule must be 
found out before the phenomena of impregnation in the plant 
in question can be determined with any accuracy. 
The received ideais as follows :—That upon the stimulus of 
the secretion of the stigma upon the pollen-grain a tubular 
prolongation of its internal membrane is ejected and thrust 
between the papille and superficial cells of the stigma; that 
this tube reaches the central tissue, and finally gains the 
ovule—and all along the course the tube acts as the pipe 
through which the granular fovilla, spermatic fluid, and its 
granules, pass from the pollen-grain to the ovule ; whether 
the theory that in the ovular end of the pollen-tube the 
future embryo is developed holds good or not, the theory of 
the descent of the contents of the pollen-grain has always 
been inferred. 
I wish to be understood that I am now about to speak of 
Tigridia alone, and that I believe that the following processes 
occur in all Monocotyledonous plants, with long styles.t The 
experimenter must remember, before he follows the path of 
these investigations, that water influences the pollen-tube in 
the following manner—it swells out the tube between the 
denser and solid parts in the axis of the tube and the tube- 
wall; it moreover puts an end, generally speaking, to the 
movement of the granules, but oil or glycerine will give a 
good idea of the normal size of the tube. 
The mechanical ideas of the primary formation of the pollen- 
tube must be abandoned ; it is essentially a vital process, and 
* Allan Maclean, M.D., of Colchester, one of the greatest raisers of 
hybrids and a most careful observer. 
+ The phenomena can be readily traced in the Crocus. 
VOL. VI.—NEW SER. B 
