Johnson : • Sexuality in Plants 



11 



the mosses (Sphagnum and Marchantia) 

 and declared his behef that they are not 

 infusoria, but are the male fertilizing 

 cells. At this time also the zoologists 

 of the day were making the first 

 detailed studies of the spermatozoa of 

 animals. Barry (1844) had seen a 

 spermatozoon within the egg of the 

 rabbit ; Leuckart ( 1 849) saw them enter 

 the frog's egg, and then, in 1851, Bischoff 

 and Allen Thompson proved that 

 fertilization is accomplished by the 

 actual entrance of the spermatozoon 

 into the egg. A no less important influ- 

 ence, in stimulating the botanical work- 

 ers on the problem of fertilization, was 

 the magnificent work of Hofmeister, 

 on the reproductive structures of the 

 mosses, ferns and conifers. By these 

 splendid researches he had indicated to 

 men of less insight, and less compre- 

 hensive imagination, just the points in 

 the life cycles of plants where the 

 critical phases of the reproductive 

 process are to be sought. 



The first step toward the demonstra- 

 tion of a union of two masses of living 

 substance at fertilization resulted from 

 the study of a group of plants in which 

 sexuality had not hitherto been proven 

 or even generally admitted — namely, 

 the algas. It had, however, long before 

 been suggested in the case of Spirogyra 

 by Hedwig (1798) and Vaucher (1803). 



STUDY OF ALG^. 



The alga; were in fact especially 

 advantageous for the study of fertiliza- 

 tion, since the development and behavior 

 of the reproductive organs and cells 

 could, without elaborate preparation, 

 be readily seen under the microscope, 

 and often followed through in living 

 material. Thus Thuret, in 1853, for 

 the first time saw the active sperms 

 attached to the egg of Fucus, and in 1854 

 proved experimentally that only eggs 

 to which spermatozoids have had access 

 will germinate. He thus demonstrated 

 in this alga the correctness of Unger's 

 unsubstantiated surmise (1837) thac the 

 spermatozoids are the male fertilizing 

 cells. In Q^dogoniuni, Pringsheim, in 

 1856 (p. 9), watched the spermatozoid 

 push into the receptive tip of the living 

 egg and saw the characteristic oospore 



wall formed in consequence. This, 

 except for the less satisfactory observa- 

 tions made on Vaucheria by the same 

 worker a year previous, is the first case 

 recorded of the observation of, the actual 

 union of male and female cells in any 

 plant. Such a union of the protoplas- 

 mic masses of the two sexual cells was 

 soon shown to be a characteristic feature 

 of fertilization in a number of algag. 

 Thus de Bary saw it in Spirogyra (1858), 

 and Pringsheim (1869) repeatedly ob- 

 served the gradual fusion of the motile 

 gametes of Pandorina. It was nearly 

 30 years later, however, that this phase 

 of fertilization was first seen in seed- 

 plants by Goroschankin and Strasburger. 



LACK OF PROPER METHODS. 



The workers on this problem were on 

 the lookout for further details of the 

 process of fusion, and even knew rather 

 definitely what they were looking for, 

 but failed to discover it from lack of 

 proper methods of preparation of ma- 

 terial. Thus, e. g., Strasburger, in 

 1877, carefully studied the process of 

 conjugation in Spirogyra and found 

 that "Hautschicht fuses with Haut- 

 schicht, Kernplasma with Kernplasma" 

 — "The chlorophyll bands unite by 

 their ends" — and then goes on to say 

 of the feature that evidently interested 

 him most, "the cell nuclei of both cells, 

 however, become dissolved; the copula- 

 tion product is without a nucleus." 

 Two years later, Schmitz (1879), when 

 studying hem.atoxylin-stained material 

 of this alga, was more fortunate. He 

 saw the two nuclei in the zygote, as he 

 says, "approach nearer and nearer, 

 come into contact and finally fuse to a 

 single nucleus." This observation by 

 Schmitz is an important one, for in it 

 we have the first clear statement that 

 the nucleus of the male cell passes over 

 intact to the female cell, there to fuse 

 with the female nucleus. 



Strasburger had, it is true, seen a 

 second nucleus fusing with that of the 

 egg in the archcgonia of Picea and Pinus 

 in 1877. He did not, however, really 

 know the source of this second nucleus, 

 though he suspected some relation to 

 those that are present earlier in the tip 

 of the pollen tube. These tube nuclei 



