Mathewson : Pollen-tube in Houstonia 48!) 



Histology 



Houstonia 



mm. wide in its longer axis, and about 1.3 mm. deep (figure 1). 

 The locules, as in the case of Diodia and Ricliardsonia, are separ- 

 ated by a partition of two portions. The lower portion arises, as 

 Lloyd has shown, from the floor of the ovary. The original 

 single ridge gives rise to two club-shaped placentae, one in each 

 locule. Each placenta soon begins to show a number of protub- 

 erances — the primordia of the ovules. The style is single, with 

 two stigmas, and arises by the concrescence of two ridge-like 

 fundaments which develop laterally and opposite to each other on 

 the inside of the hollow torus. During this concrescence a trans- 

 verse ridge is formed on the inside of the ovary roof which by 

 growing downward until it meets the ridge arising from the floor, 

 ultimately divides the originally single ovarian chamber into two 

 locules. The main point concerning the ovule is that there is no 

 integument whatever at any stage, and as a result the micropyle 

 is entirely wanting. The ovules, usually at least 15 in each 



* 



locule, are very small, averaging about 70 [i long by 60 fi deep. 

 They are when mature somewhat bowl-shaped with the concave 

 side toward the placenta. The funicle is very short. The ovule 

 conforms, broadly speaking, to the campylotropous type. The 

 embryo-sac lies buried about midway in the ovule with its slightly 

 curved longer axis at right angles with the funicle, coincident 

 with the longer axis of the ovule. 



Behavior of the pollen-tube 



The two stigmas are furnished with numerous club-shaped 



papillae (figure 1), which are found over their entire surfaces. 



These papillae are formed by the outward bending of superficial 

 cells. The pollen-grains average 15 to 17 ji in diameter, and are 

 about twice the diameter of the papillae. They have numerous 



germ -pores. 



As a rule the tube emerges from the pollen-grain on the side 

 toward the papilla, but there are many exceptions to this. In 

 some cases the pollen-tubes have been observed to emerge 

 through a germ-spot diametrically opposite to the point of con- 

 tact with the stigma, growing down upon the surface of the grain 



