274 IOWA ACADEMY OF SCIENCE Vol. XXV. 11)18 



allowed to go hig-her than three decrees above the melting point 

 of the paraffin, the tissues of the buds l)ecanie hardened and 

 brittle and could not be sectioned. 



By being very ■careful in running up the material, it was 

 found possible to get good sections in paratfi i from buds taken 

 at any time during the year. By using cedar oil in clearing and 

 dehydrating, the material was more easily sectioned and by the 

 use of cedar oil it is probable that all could have been sectioned 

 on the rotary microtome, whereas without the use of the cedar 

 oil it was necessary to cut some of the buds during the winter 

 with the silide microtome. In tracing the differentiation of flower 

 buds from leaf buds and in studying the development of the 

 floral organs the sections were cut from 10m to 25^. In studying 

 the formation of sporogenoiis.tis.sues the material was sectioned 

 as thin as 8f^. 



In general all but the last two sets were stained with Dela- 

 ficld's haematoxylin according to the procedure recommended 

 by Chamberlin (6). It was found that ten minutes staining 

 gave the tissues a heaty ovei-stain which gave excellent differ- 

 entiation to the different flower tissues when destained in 70 per 

 cent acid alcohol. In the last two sets the iron alum haematoxy- 

 lon facilitated the study of mitosis which was taking place 

 at that time. 



In order to make a detailed comparative study of the various 

 stages of development shown by the slides, at first it was thought 

 best to make camera lueida drawings (x60) of the various 

 stages. After albout two hundred different stages had been 

 drawn and studied, it was found that measurements could be 

 used quite well in comparing the relative development of buds. 

 The floral organs develop acropetally and their primordia ap- 

 pear when the primordia of organs preceding them have reached 

 a cert'ain length. The width of the crown of leaf buds was 

 found to be less than .14 mm. during the period that flower buds 

 were being differentiated. Wlien the crown of a flower bud 

 attained a width of practically .27 mm., then the differentiation 

 of the individual flowers began. From the time of its differen- 

 tiation until the primordium of the calyx appeared, the ter- 

 minal flower increased in width from .16 mm. to .24 mm. When 

 the calyx primordium attained a height of .11 mm. and the 

 receptacle a width of .34 mm. then api>eared the primordium 

 of the corolla closelv followed b\- tliat of the stamens. The 



