290 Beer, Development of the pollen grain and antlier of some Onagraceae. 
methylene blue and fucbsin are all described as pectic stains 
which leave callose uncoloured. I have found them all to st am 
tbe mother-cell walls although not nearly so deeply as tbe pectic 
membranes. 
The origen of callose has forrned tlie subject of repeated 
discussion. In the case of the callose of the Sieve-tubes some 
have asserted that this substance arises from the transformation 
of pre-existing cellulose wlrilst others believe it to be a direct 
product of protoplasmic activity originating without any relation 
to cellulose or other fore-runner. Hill in his account of the 
sieve-tubes of Pinus , takes up an intermediate position and 
believes that callose may originate sometimes directly and 
sometimes indirectly 1 ). 
In the case of the callose contposing the pollen mother-cell 
walls there can be no doubt concerning its ntocle of origen. 
It has already beeil nrentioned that- in the very young 
anther the walls of tlie primary sporogenous cells are poorer in 
cellulose than tlie otlier tissues of tlie anther. In soniewhat 
older anthers, but still long before the mother-cell wall may he 
expected to appear, the membranes of the sporogenous cells no 
longer sliow any traces of cellulose. Even after treatment with 
dilute acid and alkali — as recommended by Mangin — I was 
unable to demonstrate any cellulose in tliese walls. 
It is within tliese walls tliat the callose layer is developed. 
Ihere is, here, no disappearance of either cellulose’ 2 3 ) or pectose 
to account for a transformation of these substances into callose. 
Whatever may be the explanation of the formation of callose 
in sieve-tubes, I think there can be no doubt that in the case 
of the pollen-mother-cells the callose is derived directly from 
the activity of the protoplast without the intermediation of 
cellulose. 
Eacli mother-cell now divides to form the four special- 
moth er-cells. The mitotic figure is ratlier small and not well 
adapted for studying the details of nuclear division. 
I will content myself, therefore, with stating that in Oeno- 
thera longiflora the numher of chromosomes which appear at 
tlie first and second divisions of the pollen mother-cell is seven. 
They are so small in size that I can only distinguisli them as 
soniewhat irregulär granules; whether they have a definite and 
constant shape peculiar to eacli division (as seems likely) could 
not be certainly determined (Figs. 5—9)> In the somatic divi¬ 
sions (which I liave studied in the wall-cells of the anther) the 
chromosomes liave the form of curved rods which are crowded 
9 :Ti ie Histology of tlie sieve-tubes of Pinus“. (Ami. of Bot. Yol. XV. 
1901. p. 597.) 
2 ) Tlie cellulose is lost sight of in tlie walls of tlie sporogenous cells 
far too long before tlie callose appears for tliese substances to liave any 
Connection with. one another. Moreover tlie cellulose which occurs in tlie 
3 r °ung sporogenous wall is nierely a trace and could not possibly account 
for the massive callose wall. 
