MOVEMENT OF SPERMATOZOIDS. 55 
scalpel or razor and transferred to the microscopic slide. In many 
cases the writer succeeded in cutting off the tubes nicely by placing 
the tip of the nucel]lus with the pollen tubes uninjured on the slide in 
sugar solution under a dissecting microscope and while holding it with 
forceps severing the tubes by a lateral cut. In this way one may fre- 
quently get uninjured spermatozoids swimming free in the solution, 
and it is then a striking sight to observe them. It is difficult to believe 
that the little opaque white spheres, which can be seen very easily 
with the unaided eye and can even be observed to move around, are 
really spermatozoids. It is not a difficult matter to obtain the sper- 
matozoids moving in Zama, the writer having observed hundreds of 
them living and moving. He hasshown them to many friends, includ- 
ing some twenty of the Washington botanists. 
In remoying the nearly mature pollen tubes the spermatozoids are 
found to be in various stages of development, as would be expected. 
In many cases tubes have been observed, before cutting them off, in 
which the two spermatozoids had pulled apart and were swimming free 
in the protoplasm. In some instances their movement in the pollen 
tube, before it is injured, can be observed with the aid of a hand lens. 
This was first noticed by my colleague, Dr. Erwin F. Smith, in material 
which he was looking over with the writer, and was later observed by 
the writer in many instances. 
Evidently this is what occurs normally in the development of the 
spermatozoids, just before fecundation, as numerous instances have 
been found in prepared sections of material, just at the time of fecun- 
dation, in which the spermatozoids had broken loose from the stalk 
cell, pulled apart, and were swimming free in the pollen tube (fig. 68). 
Their lively motion probably has considerable to do with the bursting 
of the pollen tube when they are discharged in the prothallial cavity 
over the archegonia in the normal course of fecundation. In many 
instances tubes which were cut off and placed in sugar solution were , 
much younger and showed the prothallial apparatus entire, exactly as 
shown in sections. The second prothallial cell inside of the stalk cell 
in such instances showed very plainly, being of a darker color than the 
latter. The nuclei in these two cells, however, could not be discerned 
in the living material, probably owing to the surrounding starch, ete. 
The two spermatozoids in such tubes remained attached, though appar- 
ently matured. When mature pollen tubes of this nature are cut off 
without injury and placed in sugar solution the prothallial cell, stalk 
cell, and spermatozoids can at first be seen to bave their normal shape. 
In a few minutes, however, when the sugar has had time to diffuse 
into the pollen tube the spermatozoids gradually begin to move. A 
few cilia start the movement, contracting very slowly at first: then 
gradually the other cilia begin to move and the rapidity of the motion 
increases until soon all of the cilia are vibrating so rapidly that they 
