THE SEED PRODUCTION OF PIN US SYLVESTRIS. 19 



At this period it is not uncommon to find abortive 

 pollen grains ; some few have not developed a tube, others 

 have grown a tube, but the body- and stalk-cells have 

 come to grief, thus rendering them sterile. 



Ovules may occasionally be found in which the whole 

 of their tissue is breaking down : these have not been 

 pollinated, or if pollinated the pollen has not germinated. 



By the third week of April the gametophyte has 

 reached a diameter of over 300 microns ; its nuclei are 

 still parietal — they may have divided once since their last 

 division in March. It is not until the second week of 

 May that these nuclei divide rapidly and begin to fill the 

 cavity from the parietal layer inwards ; some days before 

 the cavity is filled a layer of cells is organised at the 

 nucellar end of the gametophyte distinctly different from 

 those elsewhere, their walls are thicker, their cytoplasm 

 denser, and their shape more cubical ; this layer of cells 

 gives rise to the archegonia (fig. 4). It usually becomes 

 four cells deep before the archegonia are sufficiently large 

 to be recognised as such ; they grow rapidly, and soon 

 occupy as much space as any four of the adjoining cells ; 

 they now divide, and a small cell is cut off at the dermal 

 end, from which will arise the neck-cells of the archegonia 

 (fig. 5). At this stage the archegonia are about 55 microns 

 in length, and 22 microns wide. 



The number of archegonia initiated appears to be 

 either four or eight, for in fifteen gametophytes in which 

 the archegonia are very young, and in which they can 

 readily be counted, there are nine with four archegonia 

 and six with eight archegonia. Here are definite 

 numbers, suggesting that they arise from. one mother-cell, 

 the difference being one division only. All the arche- 

 gonia initiated certainly do not reach maturity, for in 

 various stages of their development they may be found in 



