114 REPORT — 1851. 



produces in this situation tlie leafy stem growing upwards, and the adventi- 

 tious root turning downwards. The pro-embryo is at first distended like a 

 sac, and finally broken through on the one side by the first leaf, on the other 

 by the adventitious root ; upon it may be observed the numerous abortive 

 ovules, with their embryo-sacs filled with yellow contents ; part of its cells 

 grow out into radical hairs. Dr. Mettenius several times saw two young 

 plants produced from one spore; the ends of their axes lay close together, 

 and separated inside the cavity of the spore. No account is here given of 

 the characters exhibited by the small spores, or of anything like a process of 

 fertilization ; yet we have indicated in the foregoing description of the so- 

 called ovules, a clear analogy between these bodies and the so-called ovules 

 of the Ferns and Rhizocarpese. These points will be referred to again at 

 the close of the report. 



In a review of Dr. Mercklin's essay on the reproduction of the Ferns, in the 

 Flora*, Hofmeister states that spiral filaments are produced from the small 

 spores of Selaginella, but does not state that he has seen them or give any 

 authority. 



Isoetacece. — The spores of the Isoetes lacustris are of two kinds, analogous 

 to those of the Lycopodiaceae ; both kinds being produced in sporangia im- 

 bedded in the bases of the leaves, but the large spores are found in great 

 numbers, not merely four in a sporangium as in the Lycopodiaceae. The 

 development of the spores was little known until the publication of an essay 

 on the subject in 1848, by Dr-CMiillerf, forming a sequel to his researches 

 on the Lycopodiaceae. Here, as in the other case, his observations on the 

 earlier stages were imperfect; but he indicated the existence of the struc- 

 tures which have since been recognized as the so-called ovules ; as also did 

 Mr. Valentine J in his essay on Pilularia. 



In his essay Dr. C. Miiller compares the complete large spore, as discharged 

 from the sporangium, to the ovule of flowering plants ; and lie describes it as 

 a globular sac enclosed by three coats, which he names the primine, secun- 

 dine, and the nucleus. The outermost coat, or primine, is stated to be com- 

 posed of a thick cellular membrane exhibiting a raised network of lines, which 

 give it the aspect of a cellular structure, but are in reality analogous to the 

 rnarkings on pollen-grains. The outer surface exhibits the lines indicating 

 the tetrahedral arrangement of the spores in the parent cell, as in Selaginella, 

 and it is at the point of intersection of these that the membrane gives way in 

 germination. The next coat, or secundine, is another simple membrane lining 

 the first. The nucleus is a coat composed of delicate parenchymatous cells, 

 but among these are found groups of peculiar character. These are de- 

 scribed as consisting of a large cell divided by two septa crossing each other 

 at right angles, projecting from the general surface, being either oval in the 

 general outline, or having four indentations opposite the cross septa, so as to 

 give the appearance of the structure being composed of four spherical cells. 

 The cells surrounding them are of irregular form, different from the gene- 

 rally six-sided cells of the rest of the nucleus. Many of these groups occur 

 on the nucleus, always at the surface of the coat where the primine and se- 

 cundine afterwards give way, scattered without apparent order over it, but 

 one always near the point of the opening. To these structures Dr. Miiller 

 did not attribute any important function, explaining them merely as produced 



* Flora, 1850, p. 700. 



t Botanische Zeitung, April and May, 1848 ; Annals of Nat. Historj', 2nd ser. vol. ii. 1848. 



t Linnxan Transactions, vol. xvii. 



