Embryology. 221 



rface are comparatively few, and so small as to act with 

 ' ^6 slowness, when the air is dry ; so that in proportion to 



aridity of the air, and the heat to which such plants are 

 wjosed, is their reluctance to part with the food they contain. 

 They digest and redigest it with extreme slowness, and may be 

 ^y said to live upon themselves during all those months 



>n they cannot feed upon the soil or the atmosphere. 



Ladies' Botany. 



EMBRYOLOGY. 



The peculiar construction of the embryo of the Cistaceae is 

 alluded to on page 210. The following notice, by Dr. Lindley, 

 of this peculiarity, and incidentally of the method in which it 

 is supposed that the impregnation of seeds is effected, will 

 show the minute care and patience which have been devoted 

 to this obscure subject. 



The ovule of the Cistaceae has a perforation or foramen at 

 its point; all ovules have such a perforation, but not all in the 

 same place. In most ovules it is next the base ; in a few only 

 does it exist at the point, as in the plants before you. The 

 use of the foramen is not a little curious. You are aware that 

 when the ovule is first formed, it is no more than a mass of 

 pulp, in which little or no organization can be detected inter- 

 nally; but, in process of time, a small, cloudy speck forms in 

 this pulpy interior, and keeps growing larger and larger, till at 

 last it becomes an embryo. It has been observed that the 

 speck always first becomes visible next the foramen ; and 

 there is great reason to believe that in reality the speck is in- 

 troduced into the ovule through the foramen. Further, it is 

 supposed that it is in the anther that this speck is first formed ; 

 that it originates in the inside of a grain of pollen ; that when 

 the pollen falls upon the stigma, the former puts forth an ex- 

 cessively fine tube, much finer than the most delicate hair ; that 

 the tube passes down the style, and continues to lengthen till it 

 reaches the foramen; that the contents of the grain of pollen 



