EXPLANATION OF TERMS. 



483 



Median wall. In Archegoniatae : wall in 

 a plane at right angles to the basal 

 wall dividing proembryo into lateral 

 halves. 



Medullary ray. Radiating vertical band 

 of parenchyma in a stem ; is of two kinds; 

 (a) primary : extending from pith to 

 cortex ; (b] secondary : of all degrees of 

 less extent than primary. 



Medullary sheath. Protoxylem and tissue 

 in zone with it immediately surrounding 

 the pith in a stem with secondary thick- 

 ening. 



Mericarp. Portion of a fruit separating 

 as a distinct fruit. 



Meristem. Actively dividing cell tissue. 



Mesocarp. Middle layer of a pericarp. 



Mesophyll. Parenchymatoustissuebetween 

 the epidermal layers of a flat leaf-lamina. 



Metoecious. Same as heteroecious. 



Micropyle. Canal bounded by the integu- 

 ment of the ovule leading to the apex of 

 the nucellus. 



Microsporangium. Sporangium contain- 

 ing microspores. Comp. macrosporan- 

 gium. 



Microspore. Small asexually produced 

 spore compared with others belonging to 

 same species. Comp. macrospore. 



Microzoospore. Small zoospore compared 

 with others belonging to same species. 

 Comp. macrozoospore. 



Monocarpellary. Composed of one carpel. 

 Comp. polycarpellary. 



Monocarpic. A plant producing fruit only 

 once and then dying off after fruiting 

 is termed monocarpic. Comp. poly- 

 carpic. 



Monocarpous. A flower in which the 

 gynaeceum forms only one ovary whether 

 simple or compound is monocarpous. 

 Comp. polycarpous. 



Monoclinous. Of flower : same as her- 

 maphrodite. 



Monoecious. Having male and female 

 organs on the same individual ; in 

 Phanerogams the flowers are unisexual. 

 Comp. dioecious. 



Monomerous. An ovary formed of one 

 carpel only is monomerous. Same as 

 monocarpellary. Comp. polymerous. 



Monopetalous. Same as gamopetalous. 



Monopodium. An axis of growth which 

 continues to grow at the apex in the 

 direction of previous growth, while lateral 

 structures of like kind are produced 

 beneath it in acropetal succession. Comp. 

 dichotomy. 



Monosepalous. Same as gamosepalous. 



Monospermous. Having one seed. Comp. 

 polyspermmis. 



Monosymmetrical. Same as zygomor- 

 phous. 



Mucilage slit. In Anthoceroteae : slit 

 on the under surface of thallus with no 

 special guard-cells and leading like a 

 stoma into an intercellular space filled 

 with mucilage (mucilage-cavity). 



Mycelium. Vegetative hyphae of Fungi 

 spreading in or on the substratum. Same 

 as spawn. 



Nectary. Any organ secreting nectar. 



Neutral zone. In Characeae : the line, 

 marked on the external stationary layer 

 of the protoplasm utricle of a cell by 

 the absence of chlorophyll-corpuscles, 

 where the ascending and descending 

 portions of rotating protoplasm flow 

 alongside one another in opposite direc- 

 tions. Called also indifferent line. 



Nucellus. Body of the ovule (macro- 

 sporangium) containing the embryo-sac 

 (macrospore). 



Nucleus of the oosphere. Nucleus in 

 oosphere (female pronucleus) with which 

 a sperm-nucleus (male pronucleus) coal- 

 esces to form a germ-nucleus. 



Nucule. In Chara : female sexual organ. 



Nut. Same as glans. 



Nutlet. Loosely used term for a small 

 monospermous dry indehiscent fruit 

 whether formed as an independent achene 

 or as a mericarp of a schizocarp. 



Obdiplostemoiious. An androecium is 

 obdiplostemonous when the stamens are 

 arranged in two whorls, those of the outer 

 whorl alternating with the sepals and 

 being therefore opposite to the petals 

 (antipetalous or coralline stamens), those 

 of the inner whorl alternating with the 

 petals and being opposite to the sepals 

 (antisepalous or calycine stamens). 

 Comp. diplostemonous. 



Oogamous. Conjugation in which the two 

 coalescing gametes are of dissimilar form 

 is oogamous. Comp. isogamous. 



Oogonium. Female sexual organ usually 

 a more or less spherical sac without the 

 differentiation into neck and venter of 

 archegonium, and containing one or more 

 oospheres (ova). The oospore does not 

 divide to form a proembryo within the 

 cavity of the oogonium on the parent plant. 



Oophore. In Archegoniatae : same as 

 oophyte. 



Oophyte. In Archegoniatae : segment or 

 stage of life cycle of a plant that bears 

 sexual organs. Same as oophore. Comp. 

 sporophyte. 



Oosphere (egg, ovum). Naked nucleated 

 spherical or ovoid mass of protoplasm 

 which, after the sperm-nucleus has coal- 

 esced with its nucleus, developes the 

 oospore. 



I i 2 



