FERTILISATION OF THE OVULE 



723 



sections made with a sharp razor ; the ovule should not be allowed 

 to dry up, and the section should be removed from the blade of the 

 razor by a wetted camel-hair pencil. The tracing downwards of the 

 pollen-tubes through the tissue of the style may be accomplished by 

 sections (which, however, will seldom follow one tube continuously 

 for any great part of its length), or. in some instances, by careful 

 dissection with needles. Plants of the Orchis tribe are the most 

 favourable subjects for this kind of investigation, which is best 

 carried 011 by artificially applying the pollen to the stigma of several 

 flowers, and then examining one or more of the styles daily. ; If 

 the style of a flower of Epipactis,' says Schacht, 'to which the pollen 

 has been applied about eight days previously, be examined in the 

 manner above mentioned, the observer will be surprised at the 

 extraordinary number of pollen-tubes, and he will easily be able to 

 trace them in large strings, even as far as the ovules. Viola tricolor 

 (heartsease) and Ribes nig rum and ruin-urn (black and red currant) 

 are also good plants for the purpose ; in the case of the former plant 

 withered flowers may be taken and branched pollen-tubes will not 

 unfrequently be met with.' The entrance of the pollen-tube into 

 the micropyle may be most easily observed in orchidaceous plants 

 and in Eu]>hriiii<. it being only necessary to tear open with a needle 

 the ovary of a flower which is just withering, and to detach from the 

 placenta the ovules, almost every one of which will be found to have 

 a pollen-tube sticking in its micropyle. These ovules, however, are 

 too small to allow of 

 sections being made, 

 whereby the origin of 

 the embryo may be dis- 

 cerned ; and for this pur- 

 pose, GSnothera (evening 

 primrose) has been had re- 

 course to by Hofmeister. 

 whilst Schacht recom- 

 mends Lathrwa squam- 

 aria, Pedicularis palus- 

 tris, and particularly 

 Pfd icttlctr is syl/oa t ica . 



We have now, in 

 the last place, to notice 

 the chief points of inter- 

 est to the microscopist 

 which are furnished by 

 mature seeds. Many of 

 the smaller kinds of 

 these bodies are very 

 curious, and some are very beautiful objects when looked at in their 

 natural state under a low magnifying power. Thus the seed of the 

 poppy (fig. 566. A) presents a regular reticulation upon its surface, 

 pits, for the most part hexagonal, being left between projecting walls ; 

 that ofthe pink (1 )) is regularly covered with curiously jagged divisions, 

 every one of which has a small bright black hemispherical knob in its 



3 A -2 



FIG. 566. Seeds as seen under a low magnifying 

 power: A, poppy; B, Amaru nthiin [prince's 

 feather); C, Antirrhinum inajits (snapdragon); 

 D, DiantJtns (clove-pink) ; E, Bigiwuia. 



