228 BOTANY. 



young pollen-sacs undergo division into four parts, which 

 become rounded and covered with a double coat or wall. 

 The outer coat is often much thickened, and may be rough- 

 ened by ridges or prickles (Fig. 128). 



483. The pollen-cells germinate in moisture, by sending 

 out a tube which is a prolongation of the inner coat. In 

 some cases there are cells or nuclei in the cell or tube^ evi- 

 dently representing the first stage (prothallium) in its last 

 stages of suppression. The protoplasm of the cell passes 

 freely down the tube to its extremity. 



484. The ovule-bearing leaves of Angiosperms bear still 

 less resemblance to ordinary leaves than do the stamens. 

 In the simpler cases the young leaf becomes curved so that 

 its edges touch and finally grow together, forming the 

 ovary, which usually tapers above into a style or stalk sup- 

 porting a glandular structure, the stigma (Fig. 127, n). The 



whole ovule-bearing organ, com- 

 posed of ovary, style, and stigma, 

 is usually known as the pistil. In 

 many plants several pistils grow 

 together, and thus form a coro- 

 ^ ,„ „ , pound pistil. 



Fio. 189.— very young ovules. * 

 »c, OTUle-body ; sc inner, and pr, 485. The OVuleS gTOW UpOn the 

 outer, coats just beginning to or 



MO MmS °™'*'^'*'^' ''^^^^^ inner (i.e., upper) surface of the 

 leaf which forms the ovary, or at 

 its base (Fig. 127), or more frequently upon its margins. 

 At first it is a simple rounded outgrowth of a few cells; as 

 it grows older a circular ridge arises upon it, which often 

 is soon followed by another (Fig. 129, A and B). These 

 ridges grow out and upwards so rapidly that they overtake 

 and enclose the ovule-body, leaving but a small opening or 

 pore. 



