BOT.— Vol. II.] OSTERHOUT— AGAVE. 263 



characterized by the presence of the genetic fibres will be 

 called the genetic stage, and may be defined as lasting from 

 the first appearance of the genetic fibres to the time when 

 the cones are fully developed, and the nuclear wall has dis- 

 appeared. As in many cases these two processes do not 

 occur simultaneously, it should be understood that the ge- 

 netic stage is not ended until both are completed. 



The genetic fibres are attached to both the nuclear wall 

 and the spindle wall; the point of insertion on the latter is 

 marked by a granular enlargement (see figs, 4 to 10). 

 They may be derived in part from the original radial fibres 

 of the cytoplasmic layer abutting on the nucleus, but to a 

 great extent they appear to be new formations, since they 

 are much more numerous than the original radial fibres. 

 The fact that the nucleolus disappears about this time is in 

 accord with Strasburger's assumption that its substance is 

 used to furnish material for the kinoplasmic fibres {^cf. 

 Strasburger, 1900, page 124,/*. ; 1897, page 2>1^,f.; 1895). 



During the development of the genetic fibres, the genetic 

 layer gradually widens, and the radial arrangement of the 

 cytoplasm becomes less pronounced (figs. 3 to 7). In the 

 meantime, the irregular fibres lying outside the spindle wall 

 have undergone a change similar to the genetic fibres inside 

 the wall. The former will be called the exterior fibres to 

 distinguish them from the genetic fibres. The granules in 

 the exterior fibres become crowded, and fuse just as in the 

 genetic fibres; the fibres become smoother, straighter, 

 thicker, and less granular in appearance, staining deeper 

 and deeper violet. At the same time, they gradually take 

 on a more radial arrangement, and grow longer, until they 

 finally present the appearance seen in fig. 7. The stages in 

 this process are clearly seen in figs. 2 to 7. These fibres 

 appear to be the result of a transformation of the fibres of 

 the cytoplasmic network, the process of transformation 

 proceeding from the spindle wall outward. 



It is in connection with certain of these exterior fibres 

 that the cones are formed. It is usually where the more 

 conspicuous exterior fibres (those which extend to the 



