16 STUDIES IN HISTOLOGY. 



The 2iistil requires little special study, except in regard to its 

 development. It will be well to examine the conductive tissue 

 of the st} T le and trace it down to the ovarian walls. (Other 

 minute matters connected with the stamens and pistils are con- 

 sidered under "Fertilization.") 



V. DEVELOPMENT or THE FLOWER. 



From the youngest flower-cluster of any plant having indeter- 

 minate inflorescence, for instance that of Lepidium or Capsella, 

 cut squarely off a short piece of the tip, place it on a glass slide 

 in a little alcohol, in order to remove the air, and cover with 

 thin glass. (If the student has an air-pump, the specimen can 

 be placed at once in water on the slide, and then subjected to 

 the action of a partial vacuum, which will of course free the 

 whole preparation from any air-bubbles.) After the air has 

 been removed, add water, and if the specimen requires clearing, 

 as is usually the case, some potassa. On gently warming the 

 slide the specimen will grow somewhat darker, but after a time 

 will be made tolerably clear. If not, proceed as directed in 25. 

 The specimen, if a good one and well prepared, ought to show 

 all the relations of the several flowers of the cluster to each 

 other. Prepare a second specimen by removing the flowers in 

 succession under the dissecting lens, beginning with the larger, 

 and placing them in a row which will comprise all the stages of 

 development. With the material thus obtained, which it is well 

 to keep moist with glycerin, the examination of all the different 

 parts can be successfully carried out. The stud}* will be far 

 more instructive if the student makes a parallel series with an 

 allied species. Comparison of the two species above mentioned 

 shows exactly when and where some of the parts are arrested in 

 development. 



VI. DEVELOPMENT OF THE POLLEN. 



The examination of the anther for this study should begin at 

 a very early stage in the growth of the flower, and particular 

 attention should be given to the cells which line the pollen cavi- 

 ties. Great advantage is gained from the skilful employment 

 of staining agents, by which the parts are brought out more 

 clearly (see 77 et seq.\ All changes in the character of the 

 nucleus of the grains during their differentiation demand for 

 their identification the use of staining agents without the pre- 

 vious application of potassa. 



