DEVELOPMENT OP THE FLOWER. 



167 



very tip of the raceme is to be cut squarely across and placed 

 with a drop of water under a cover-glass, when some of the young- 

 est flowers can be seen either standing vertically or slightly in- 

 clined. The air can be drawn 

 out from the specimen by 

 placing the slide for a min- 

 ute under the air-pump ; the 

 outlines of the floral organs 

 will then be distinct. 



469. A still better method 

 is to make tolerably thick 

 vertical sections of separate 

 flowers, one of which in 

 each flower must be through 

 the median line ; and then, 125 



arranging the sections l in 



their proper sequence, clear them for examination either by the 

 use of potassic hydrate (as directed in 24), or b}- the following 

 method, recommended by Stras- 

 burger as applicable to many cases 

 of thick masses of soft tissues : 

 Treat the part first with absolute 

 alcohol for a day or two, and then 

 place it in concentrated carbolic 

 acid, after which it becomes clear. 

 For the carbolic acid either of the 

 126 following may be substituted, 



(1) three parts of oil of turpen- 

 tine and one part of creosote, or (2) equal parts of alcohol and 

 creosote. 



By any one of these methods it is generally possible to obtain 

 preparations of sufficient clearness to exhibit in optical section 

 all the internal tissues. 



1 Pfeffer advises that the young flowers should first be tinged with anilin 

 blue, and then imbedded in a strong solution of gum-arabic (to which a little 

 glycerin has been added to prevent brittleness of the mass on drying). Then, 

 when the gum is dry, sections can be easily cut in any direction. 



FIG. 125. Lysimachia quadrifolia. Flower seen from the side, and somewhat ob- 

 liquely, the calyx being removed. At this period the parts of the corolla have not 

 coalesced : sp, place where the excised sepals were; p, petal; st, stamen. (Pfeffer.) 



FIG. 126. Lysimachia quadrifolia. Thin longitudinal section through the median 

 line of a flower, in which the organs are beginning to form. Before the sinuses of the 

 calyx, as well as before its lobes, cell-division has taken place on all sides; for instance, 

 at st, n, and x. (Pfeffer.) 



