GNETALES— WELWITSCHIA 395 



rudiments have been found, and since insect pollination has never 

 been proved for any gymnosperm, nectaries would hardly be an- 

 ticipated. 



The anthers are trilocular, resembling somewhat the sporangia of 

 Psilotum. 



Floral development.— A. longitudinal section of a strobilus, about 

 I cm. in length, shows a very complete series of stages in floral de- 

 velopment, from the beginning of the bract to nearly mature pollen. 



The first protuberance to appear below the apex of the strobilus 

 is a bract. The conical structure which soon appears in its axil is 

 the beginning of the flower, and its apex finally develops into the 

 sterile ovule. The first floral organs to appear are the bracts of the 

 perianth, soon followed by the staminal rings. Pearson says the 

 two lateral stamens appear first, followed immediately by the other 

 four, which grow faster, so that they all look alike; Church says 

 they appear simultaneously. If the two outer ones appear before the 

 other four, the appearance in succession would favor the view that 

 there are two cycles of stamens and that two of the outer set have 

 been lost. There are six vascular strands in the staminal tube, one 

 going to each filament. The fact that the two strands going to the 

 two lateral stamens are inserted lower down than the other four fa- 

 vors Pearson's view. 



As soon as the rudiments of the stamens can be recognized, the 

 integument appears as a ring about the base of the nucellus. There- 

 fore, the development is acropetal throughout. Later, there is a 

 great development of both staminal tube and the integument. Some 

 of the stages of floral development are shown in fig. 372. 



In studying the floral development, one cone was sectioned in 

 which the sterile ovule terminated the cone axis. The flower was 

 large and the pollen mother-cells had rounded off, while the next 

 flowers below were in an early sporogenous stage. 



During the elongation of the staminal tube, the reduction division 

 takes place in the pollen mother-cells, the second division following 

 the first so closely that the young microspores have a typical tetra- 

 hedral arrangement. 



