92 MARGARET C. FERGUSON 



dently the usual condition in P. austi'iaca^ P. rigida and P. 

 resmosa, but in these species, too, much variation obtains. 

 Variation in the number of neck-cells seems to be of common 

 occurrence in the Gymnosperms. It was first noticed by Hof- 

 meister in 185 1 and has recently been discussed by Coulter and 

 Chamberlain ('01). Murrill ('00) has figured considerable 

 irregularity in the number and arrangement of these cells in 

 Tsuga, while Coker ('02) shows a very marked variation in 

 Podocar^tcs. 



At first the growth of the central cell is not followed by a 

 corresponding increase in the amount of protoplasm, so that its 

 cytoplasm early presents a very vacuolate appearance. There 

 may be one large, irregular central vacuole, or delicate strands of 

 cytoplasm may extend out from the nucleus to the ectoplasm, 

 these strands meeting and fusing at irregular intervals to form 

 vacuoles of various sizes. Thus a very beautiful pseudo-alveolar 

 structure is presented. Webber ('01) describes the cytoplasm in 

 the central cell in Zamia as representing at this time a foam struc- 

 ture of great beauty. I have never observed in this or any cell 

 in Pinus a cytoplasmic structure which, according to my inter- 

 pretation, could be designated as a true alveolar or foam struc- 

 ture in the sense in which Biitschli ('94) uses the term. As the 

 central cell continues to enlarge its cytoplasm begins to develop 

 more rapidly, many strands extending out into and across the 

 vacuoles. Thus the size of the vacuoles is decreased while 

 their number is greatly increased. The central vacuole, if 

 present, may persist for a considerable time, or it may be re- 

 placed at once by smaller vacuoles (figs. 172-175). Gradually 

 the cytoplasm becomes more dense, and the vacuoles, receding 

 from the periphery of the cell, especially from its base and sides, 

 disappear last from its upper portion (figs. 176, 177). When 

 the ventral canal-cell is cut off, the vacuoles have nearly or quite 

 been replaced by a finely granular cytoplasmic reticulum in 

 which a greater or less number of larger, more deeply staining 

 granules are imbedded. These granules are frequently sur- 

 rounded by a clear court into which the protoplasmic network 

 has not extended. The number of the so-called proteid vacu- 

 oles is usually small at this time (fig. 178). 



