228 Mr. II. Giraud on the recent Doctrines 



ment of the embryo in Zea Mays. The following are the re- 

 sults which wore obtained, arranged, as by Mirbel and Spach, 

 under seven general heads, corresponding with the progressive 

 periods of the growth of the female organs*. 



First Period, — The origin of the female spike of the Zea 

 Mays, like that of all the external organs of plants, commences 

 in a simple excrescence of cellular tissue, invisible to the naked 

 eye. As it advances in age, this excrescence enlarges, elon- 

 gates, becomes conical, and is studded partially from base to 

 apex with little projections, which separately give origin to 

 others. Each group of mammillary projections is the germ of 

 a future flower ; but seldom more than one becomes developed 

 in each group, the rest being abortive. The remaining one, or 

 that which is ultimately formed into a flower, produces at its 

 circumference little thin cushions of tissue (bourrelets) in the 

 form of rims, some of which form complete circles, others only 

 semicircles ; all however being concentric. Each of these 

 little margins is quickly transformed into either a bract, a 

 glume, a carpel, an ovary, or the integument of an ovule, ac- 

 cording to the relative position which it occupies. The apex 

 of the mammillary projection constitutes at this period the 

 nucleus of the ovule. 



Second Period. — The ovarium has now 7 the form of a small 

 cup with a large orifice, and its pai ietes consist of a thin and 

 transparent membrane. The nucleus is fixed to the base of 

 the ovarium ; — an arrangement which is constant in the Mays, 

 The primine and secundine proceed from the circumference 

 of the nucleus, which they partly inclose. The first of these 

 envelopes being much shorter than the other, surrounds the 

 nucleus only at its base ; hence it follows that the endostome 

 sensibly extends beyond the exostome. 



Third Period. — The style, of which, up to this period, there 

 was not the least appearance, arises from that side of the ova- 

 rium which is nearest to the axis of the spike ; as it elongates 

 it assumes the form of a straight lamina of tissue. The ovule 

 with its two membranes, — the primine and secundine, has 



* Notes pour servir a l'Histoire de l'embryologie vegetale. Par MM, 

 Mirbel et Spach, Ann. des Scien. Nat. 2nde Serie, Botan. Avril 1839. 



