FERNS. IdT 



occurs, into a plant similar to that from which the seed was itself 

 produced. But a spore does not contain an embr^^o, l)eing filled 

 with a thick gelatinous matter instead. On germination taking 

 place this gelatinous matter swells, and expands the elastic inner 

 membrane until it ruptures the outer covering of the spore, and 

 the spore cell protrudes in the form of an elongated sac. 



Development then proceeds, through the process of cellular ex- 

 pansion and division, until a flat, leaf-like body is produced, which 

 in its turn, by a new process of growth, develops special fertilizing 

 organs through whose agency the young plant is brought into 

 existence. This form of plant life, so utterly unlike that which is 

 destined to arise from it later on, is technically called a prothallus, 

 or prothallium, meaning thereby an elongated, fliat, cellular struc- 

 ture preceding the formation of some plant structure of a highei* 

 order. This condition, in some of the lower orders of plants, is in 

 itself the perfected plant structure, as those of you who are 

 acquainted with the Marchantias, and similar plants, know. 



I will not weary you with a description of the special organs 

 which are evolved from the substance of the prothallium, nor with 

 the technical points involved in the gradual development of the fern 

 plant itself. Those of you who care to pursue inquiry in that 

 direction further Avill find the subject carefully elaborated in the 

 series of text-books by Hofmeister, Sachs, DeBary, Bessey, and 

 others. I have dwelt upon it thus far only that you might see how 

 very different from the life-history of a flowering plant, the life- 

 history of a fern is. In the one case we have a plant producing a 

 seed which in its turn reproduces directly the parent plant ; while 

 in the other we have a plant which produces an organless cellular 

 body, which produces an entirely different and independent plant 

 form, which in its turn reproduces the original parent plant. So 

 that the cycle of generations runs thus : the fern produces a spore, 

 the spore produces a prothallium, the prothallium produces a fern. 



I have here two fine charts, from Dodel-Ports' magnificent work, 

 which illustrate fern reproduction admirably. 



In Part 2, plate I, figure 5, we have a portion of a frond of 

 Aspidium Filix-vias, one of the shield ferns, a magnified portion 

 of a pinnule showing the sori, or fruit dots. Figure 1 shows a 

 cross section through a sorus wherein the arrangement of the 

 sporangia on the receptacle is plainly seen, with the over-arching' 

 indusium. Figure 2 shows a detached sporangium. The elastic 



