i6o THE LIVING CYCADS 



nuclei before walls appear, and in some species of Zamia 

 about two hundred and fifty. Doubtless the very small 

 Zamias, like Zamia pygmaea, would show a still smaller 

 number of free nuclei. 



This reduction in the number of free nuclei before 

 walls appear is significant, if we compare the Coniferales, 

 the group to which the pine, fir, cypress, yew, and other 

 familiar evergreens belong. The eggs are smaller than 

 in the cycads, and the number of free nuclei is cor- 

 respondingly smaller, in Taxus 32, in Podocarpus 16, in 

 Thuja 8, and in Pinus 4. In Sequoia, the mammoth tree 

 of CaKfornia, there is no free nuclear period, a wall 

 following the first division of the nucleus of the fertilized 

 egg, which is very small, and this condition is found in 

 all the higher plants. 



Thus it is seen that there has been a rise of the free 

 nuclear period accompanying an increase in the size of 

 the egg, and a decKne as the size of the egg became more 

 and more reduced. The series begins and ends with 

 small eggs in which a wall followed the first division of 

 the nucleus, the rise and decline of the free nuclear 

 period coming between. In determining whether a 

 certain form is primitive or advanced with respect to 

 the free nuclear feature, it is obviously necessary to note 

 whether one is dealing with a small number of nuclei 

 in an increasing or in a decreasing series. 



The similarity between this embryogeny and the 

 development of the female gametophyte — both having 

 a free nuclear period followed by the formation of cell 

 walls — often confuses students. The causes of the 

 phenomena being the same in the two cases, it is Aot 

 strange that both should show a rise and decline of the 



