104 IOWA ACADEMY OF SCIENCES. 



PoDASPH^RA OxYACANTH^E (D C), Duby On Pniniis Cerasus. 

 MiCROSPH^BA RussELii, Clinton on Oxalis^corniculata var. stricta. 

 *M. Grossulari^ (Wallr.) Lev. on Sanibucus Canadensis. New. 

 M. Euphorbia (Peck), B. & C. on Euphorbia coroUata. New. 

 M. Alni (D C), Winter on Vibumnm lentago, Si/ringia vulgaris. 

 M. QuERCiNA, (Schw.) Burrill on Quercus rubra. 



THE PARAFFINE METHOD APPLIED TO THE STUDY OF THE 

 EMBRYOLOGY OF THE FLOWERING PLANTS. 



BY H. W. NOKRIS. 



These few notes are given, not that they contain much if anything new, 

 but simply as the record of a year's experimenting. The difficulties con- 

 nected with the use of paraffine in the sectioning of plant tissue are well 

 known to all students in botanical microscopy. The cutiu, cork, etc. of the 

 cell wall resist peneti'ation. The heat necessary to melt paraffine often I'en- 

 ders the tissue too hard and brittle for successful manipulation. Free- 

 hand sectioning is often the only available method. Frequently this is all 

 sufficient. Celloidin (or collodion) is available for imbedding young and 

 soft tissues, requires no heat and its general cleanliness and easy manipula- 

 tion recommends its use whenever possible. But many plant tissues are of 

 too firm and resisting a structure to render the use of celloidin even possible. 

 Seeds in their mature condition, will not permit the use of celloidin, and 

 seem to almost defy the penetration of pai'affine. 



In attempting to study the development of ovule in the Compositte, I was 

 led to find some way of obtaining perfect series of sections through the 

 flower. The forms studied were Qrindelia squarrosa, Eelianthus anmms, 

 and a cultivated species of Ageratuni. In most of the Composita3 the tissues 

 of the flower become very i-esistant to the section knife, even at an early 

 period. The testa of the seed is not easily penetrated by reagents. The 

 peculiar structure of the ovule found in many Compositas, called endodermis 

 by Hegelmaier, becomes very hard and brittle on application of heat. 



Rowlee' obtained good sections of ripe seeds by the paraffine method, 

 after first soaking them in water twenty-four hours before dehydration. 

 Having seen his sections I determined to try some modification of his 

 method. As I did not study the mature condition of the ovule, I did not 

 soak any of the material in water. 



The tissue was hardened first in 25% and then 50% alcohol, and pre- 

 served in the latter. Then as material was needed it was dehydrated in a 

 Schultze's dehydrating apparatus into 95% alcohol, then placed in the fol- 

 lowing substances successively, one to several days each: 95% alcohol and 



ilmbedding and Sectioning Mature Seeds, Proceedings American Society Micro- 

 scopists. 1890. 



