Leaf anatomy of in situ digested Bromus auleticus and Setaria lachnea.

Percentages of foliar tissues and attack pattern undergone under ruminal digestion of Bromus auleticus Trin. ex Ness (Cebadilla Chaqueña) and Setaria lachnea (Nees) Kunth) (Moha Perenne) are descripted in the present study. Leaf samples were kept in 10 x 20 cm nylon bags with 50 + 15 µ pores, and were stored to ruminal digestion for 24 and 48 hours in a cannulated cow. Samples of the digested material were taken and prepared for their observation under a scanning electron microscope (SEM).

Five millimeter long leaf blade samples were fixed in formol aceto alcoholic solution (FAA), sectioned with a rotating microtome and stained with safranine-fast green, in order to perform the quantitative anatomic studies. A PLANIX 7 electronic digital planimeter was utilized to determine the area corresponding to each tissue. Total slow and non digestible tissues (TLDI), i.e. xylem + epidermis + bundle sheath + schlerenchyma, were determined. B. auleticus showed a higher proportion of schlerenchyma and chlorenchyma, while percentages of vascular tissues, bundle sheath and epidermis were higher for Setaria lachnea, which presents, therefore, higher TLDI tissues.

In B. auleticus phloem and clorenchyma were completely digested at 24 hours. However, in the same period of time the both epidermis were incompletely degraded. Finally, the protoxylem and both epidermis were completely digested at 48 hours. In S. lachnea the phloem, chlorenchyma and abaxial epidermis were completely degraded at 24 hours. The abaxial epidermis was completely digested at 48 hours.

Key words: leaf anatomy, digestibility, C3 and C4 grass.