BOT.— Vol.. II.] OSTERHOUT— AGAVE. 261 



The following account relates to the first division of the 

 pollen-mother-cells. The cytoplasm of the resting cell 

 presents the appearance of a network with fairly regular 

 meshes. The fibres of the network are covered to a 

 greater or lesser extent by a deposit of granular substance 

 which tends to stain somewhat more deeply with orange G 

 than the substance of the fibres. The network appears 

 practically alike in all parts of the cell. 



I. Progenetic Stage. 



During the formation of the dense chromatin thread and 

 the separation of the chromosomes the meshes of the cyto- 

 plasm become radially elongated, until they present the 

 appearance seen in fig. i. The meshes immediately sur- 

 rounding the nucleus are somewhat smaller and more 

 regular than the others. Just outside these is a layer 

 of somewhat denser and more granular cytoplasm, while 

 the peripheral layer consists of greatly elongated meshes, 

 which produce at first glance the impression of free fibres. 

 The fibres are not free, however, but are constituent parts 

 of a network; it is interesting to observe, nevertheless, 

 that a large proportion of these fibres run more or less in 

 a straight line directly to the nucleus. The layer of cyto- 

 plasm, one mesh in thickness, immediately in contact with 

 the nuclear wall, is of quite even width (see fig. i) and 

 gives rise to the genetic or spindle-forming layer; it will 

 therefore be called \h.e. progenetic laye?-^ and may be defined 

 as that layer of the cytoplasm from which the genetic layer 

 immediately arises. The stage in which this layer takes on 

 its characteristic condition will be called the progenetic 

 stage, and may be defined as the stage immediately preced- 

 ing the genetic stage, and in which preparation for the latter 

 is going oh in the cytoplasm. 



In fig. 2 the progenetic layer may be seen undergoing a 

 characteristic change: at one end of the nucleus (the 

 upper end in the figure) it retains its original form, on the 

 sides it is growing narrower, its radial fibres are becoming 

 less distinct, and granules are making their appearance 



