ABSTRACT
Structurally caryopsis of the different grass species shows a great variation. General anatomy of grass caryopsis reveals that it can be divided into three distinct parts/regions: (1) the caryopsis coat which includes the pericarp, the seed coat, and the nucellus; (2) the endosperm; and (3) the embryo. The grass embryo is highly specialized and appears as an oval depression on the flat side of the caryopsis next to the lemma. On the opposite side of the grain of the embryo is the hilum; a line marking the point of attachment of the seed to the pericarp. The scutellum is a haustorial organ, equivalent to the single cotyledon, and functions in enzyme secretion and absorption of nutrients from the endosperm. Endosperm occurs as a large elliptical structure and is usually solid and starchy.
Characteristic features like course of vascularization, presence or absence of epiblast, presence or absence of cleft and arrangements of embryonic leaves in cross section have been adapted from Reeder (1957). Other than these, pericarp, angle of embryo with respect to anterior-posterior position of caryopses, coleoptiles, plumule, mesocotyl, coleorhiza, types of epiblast, scutellum, angle of vascularization, endosperm, type of starch grains, types of aleurone layer were also taken into consideration for the study. Other significant diagnostic features were observed for the first time in caryopses anatomy. This includes: (1) Embryo placed at different angles with respect to anterior-posterior position of caryopsis. Based on this feature, angle of embryo with respect to caryopses has been measured and it could be classified into three categories: less than 130°, between 130° and 160° and between 160° and 190.° (2) Previous studies report only presence or absence of epiblast in the different species studied according to which in group Panicoideae all the members showed absence of epiblast except Chionachnae koengii, while in group Pooideae all members showed presence of epiblast except Ischanae globosa from tribe Ischaneae, Aristida adscensionsis, Aristida funiculata from Aristideae and Melanocenchris and Oropetium from tribe Chlorideae. Five different types of epiblast could be identified and categorized. This was found to be an important diagnostic feature for identification of grass species. (3) Different authors have categorized the type of scutellum into two main categories: sickle shaped and V shaped but in the present study based on the shape and further on the angle which forms the different shapes, scutellum could be broadly divided into three main categories: V shaped, U shaped, and ∆ shaped. Further 18 different types of V shaped scutellum, 5 different types of U shaped scutellum, and 6 different types of ∆ shaped scutellum were observed and categorized. Based on above characters, identification key was prepared which help to identify caryopses on the basis of anatomical features. (4) Angle of vascularization was also studied in detail and the grass species could be divided into four different categories.
Quantitative features like cross section size of caryopses, seed coat thickness, aleurone cell size, occupied % of endosperm, thickness of endosperm, occupied % of embryo, thickness of embryo, number of starch grains per endospermic cell were also observed. Species belonging to the same genera could be identified distinctly. On the basis of embryo anatomy caryopses has been divided into six categories by Reeder (1957). According to this the grass species could be categorized into the following: All Panicoideae members belonged to True panicoids except Chionachnae koengii which belonged to Oryzoid-olyroid group. Most of the members of Pooideae group belonged to Chloridoid-Eragrostoid group except Chloris montana, Chloris virgata, Sachoenefeldia gracilis belong to Bambusoid and Aristida sp., Melanocenchris jaquemontii, Orepetium villosum belonged to Arundinoi-Danthonioid group. A dichotomous key has been prepared with the help of these characteristic features and dendrogram has been prepared by using cluster analysis.
