78 
JOUENAL OF THE ROYAL HORTICULTUKxVL SOCIETY. 
PROTOPLASM : WHAT IT IS, AND HOW IT MAINTAINS 
PLANT-LIFE. 
Substance of a Lecture at Chiswick Gardens. 
By Eev. Prof. G. Henslow, M.A., V.M.H., &c. 
[June 20, 1900.] 
If a section be made of any growing shoot or root, the earhest condition 
of a hving cell reveals a delicate cell-wall, within which is a mass of 
colourless protoplasm, completely filling it, with a relatively large oval 
body, called the nucleus, in the middle. The cell-wall is really a sort of 
secretion from the living protoplasm, and consists of the three elements 
carbon, hydrogen, and oxygen in the proportions CgHioO^ ; whereas the 
protoplasm is much more complicated, in the numbers of its atoms, and 
is composed of the elements C, H, N, 0, S, and P ; nitrogen, sulphur, and 
phosphorus being additions. 
The next stage is seen when the cell has grown to a larger size and 
the protoplasm does not keep pace with it, so that it becomes hollowed 
out into " vacuoles," which become filled with watery cell-sap. It then 
appears as a sort of network, still suspending the nucleus in the middle. 
Particles can be seen moving about along the connecting threads of 
protoplasm. 
Afterwards all the protoplasm, by the union of the vacuoles, may 
come to lie on the cell-wall, and the nucleus is then carried to one side. 
Mohl in 1846 observed this condition, and called this layer of protoplasm 
the "primordial utricle." 
The next thing to notice is the structure of the nucleus, and to 
discover what part it plays in plant-life. Examined by high powers of 
the microscope, it is seen to be bounded by a delicate film. Within this 
is what looks like a tangle of knotted thread. One or more round bodies 
lie within the thread, called nucleoli. 
When a young cell is going to divide into two, the twisted thread 
breaks up into a definite number of pieces called " chromosomes," each 
being folded like a U. At this stage the bounding membrane disappears, 
and the surrounding protoplasm now presses in and places the chromo- 
somes in the middle, which arrange themselves in the equatorial plane. 
Now two star-like bodies appear, called " directing spheres," in the 
protoplasm, and between them fine lines are seen forming a spindle 
connecting the two spheres. The twelve chromosomes now divide again, 
and each half, attaching its two ends to a line of the spindle, glides along 
it till it reaches one of the poles, so that one half of the chromosomes go 
"to one pole, the others to the other pole. There the collection of chro- 
mosomes unite and form a daughter nucleus. A cell-plate now appears 
across the equator of the spindle, and is gradually extended through the 
outlying protoplasm till it reaches the walls of the cell. Thus two cells 
are made out of one. 
