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Apospory

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1903.]

On

the Cytology

of Apogamy and Apospory.

45

"

On

1, Preliminary the Cytology of Apogamy and Apospory. Note on Apogamy." By J. B. Farmer, F.E.S., J. E. S. Moore, and Miss L. Digby. Received March 24, Bead March 26,

— —

1903.

as

The phenomena of apogamy and apospory have always been regarded "short cuts" in the life history of ferns, and the fact that either

apparently

generation

may

be

directly

produced

from the

other, without the intervention of oosphere or spore respectively, has

been taken to indicate that the gametophyte and sporophyte are homologous phases in the life histories of these plants. But since the cytology of the two generations has been carefully studied, it has become recognised that the prothallial generation is composed of cells, the nuclei of which possess only half the number of chromosomes that are characteristic of the alternate sporophyte generation.

In normal cases the doubling of the number of the chromosomes effected during the transition of the

is

gametophyte to sporophyte by
is

the addition of the chromosomes belonging to the spermatozoid to

those of the oosphere,

and

this

double number

retained until they

once more become reduced to one half in the formation of the spores that introduce again the gametophyte stage of the life-cycle. It is

obviously therefore of considerable theoretical

interest

to

ascertain

how

the

irregular
It is

transitions

apogamy

are effected.

with the

known as apospory and facts of apogamy that we are

here concerned, the details relating to apospory being reserved for a future communication.

Certain species of nephrodium
are

(e.g.,

known

to produce prothallia on
is

N. pseudo-mas, var. polydactylum) which the apogamous formation

of sporophytes

of

normal instead of rare occurrence.*
received a
special

By

the

kindness of Dr.
of

Lang we...

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