176 Lawson . — The Gametophytes and Embryo of 
Coker (’02) reports a similar structure in connexion with the suspensors in 
Podocarpus. In the latter case, however, Coker describes this plug as 
cellulose. The suspensor plug in Pseudotsuga failed to give the cellulose 
reactions. It is more probably mucilaginous in composition. The position 
and evident function of this plug is brought out in Fig. 42. 
Summary and Conclusions. 
The microspore at the time of pollination is globular in form and 
differs in appearance from that of the majority of other Abietineae in the 
entire absence of bladder-like appendages. 
The mature microspore contains four cells. Two of these are repre- 
sented by the fragmented remains of two vestigial prothallial cells, and the 
other two represent the tube and generative cells respectively. 
Owing to the peculiar form of the micropyle, which has a stigmatic 
surface at the mouth, the pollen grains fail to reach the apex of the nucellus, 
but are caught at the mouth of the micropyle and here germinate. 
This pollen-receiving device and the formation of pollen-tubes so far 
removed from the nucellus is unlike anything yet reported for the Abietineae, 
and is evidently a novelty as far as the Gymnosperms are concerned. 
With the first appearance of the pollen-tube the generative nucleus 
divides, and as a result of this division two distinct cells are organized, one 
of which is considerably larger than the other. These are the body- and 
stalk-cells respectively. 
The pollen-tubes grow down the micropylar canal and attain a 
considerable length before the nucellus is reached. 
The tissue of the apex of the nucellus disintegrates in advance of 
the approaching pollen-tubes, so that the latter structures find little or 
no obstruction in their path towards the archegonial chambers. 
The division of the body-cell results in the formation of two male 
nuclei of unequal size. 
The entire nuclear contents of a pollen-tube are discharged into one 
archegonium. 
There are probably three megaspores resulting from a single mother- 
cell. Two of these are abortive and one functional. 
Upon the enlargement of the functional megaspore free nuclear division 
takes place, and this is followed by the formation of a large central vacuole. 
Completely enveloping the growing megaspore there is a single layer 
of large sporogenous-like cells which are closely packed together. This 
layer of cells, although single at first, soon becomes several layers thick, and 
eventually becomes quite loose and sponge-like — with numerous inter- 
cellular spaces — as the young prothallium increases in size. This tissue is 
regarded as sporogenous in origin and tapetal in function. 
The megaspore membrane makes its appearance at a very early period, 
