324 Saxton. — Contributions to the Life-history of 
All material for microtome sectioning was embedded through cedar-wood 
oil, and in the later material it was found possible, with frequent changes of 
paraffin, to reduce the period in the oven to about four hours. 
All microtome sections were cut with a Cambridge rocking microtome 
to a thickness of about 7 /x, and stained with either Delafield’s haema- 
toxylin or (usually) Fleming’s triple stain. All drawings were made from 
such sections except Text-fig. 1, and PL XXV, Figs. 17, 18, and 19, which 
are from hand sections, and all were made with the camera lucida. 
1. Microsporangium and Microspores. 
The position of the three sporangia on the stalk of the sporophyll is 
indicated in PI. XXV, Fig. 1. The structure of the sporangium is exactly like 
that of Callitris. The wall, when mature, consists of a'single layer of rather 
large and somewhat thick- walled cells, but in younger stages two layers of 
thin-walled cells are met with between the epidermis and the sporogenous 
tissue. The origin of these cells has not been determined, but the two 
layers are evidently derived from a single layer by periclinal divisions, and 
are probably morphologically part of the sporogenous tissue. The close 
resemblance in the stages that have been seen to the corresponding stages 
in Juniperus , as described recently by Nichols ( 17 ), makes it highly probable 
that the course of development is very similar ; in Juniperus the two layers 
of thin-walled cells to which reference has been made are clearly shown to 
be derived from the sporogenous tissue. 
Functionally they represent at least a part, and probably the whole, 
of the tapetum. 
Unfortunately, my material only includes quite young, and mature or 
nearly mature, male cones, so that stages to illustrate sporogenesis have 
been missed. 1 The mature pollen-grain (Fig. 2) is exactly like that of 
Widdringtonia and Callitris , and is uninucleate at the time of pollination, 
the nucleus being surrounded by a layer of rather large starch grains. 
As seen in section, the exine is thin and the intine rather thick ; it is very 
probable, however, that in the fresh state the real thickness of the intine is 
considerably less than appears in sections of fixed material. Observations 
on fresh pollen of related Conifers have indicated the difficulty of preventing 
considerable swelling of the intine in fixing material ; possibly the difficulty 
might be overcome with special technique. 
2. The Female Cone and the Ovule. 
Text-fig. 2 is a transverse section across a young cone, passing through 
the base of the ovules. The close resemblance of sterile and fertile scales, 
when young, is apparent, the innermost whorl bearing generally two ovules 
1 Since the above was written I have obtained late stages of spore-formation from cones procured 
from Kew through the kindness of Mr. L. A. Boodle. These have shown that the tetrad of spores is 
formed in a mother-cell which, unlike that of Pinus, does not become partitioned. 
