Johnson: Sexuality in Plants 



followed these tubes through the style 

 to the microp^de of the ovule. At about 

 this time also, Jakob Matthias Schlci- 

 den (1838) took up the study of this 

 same problem. He was a man _of 

 vigorous intellect and great versatility, 

 who sometiincs misinterpreted what he 

 saw, but who proved a most stimulating 

 opponent to a number of other workers 

 who did observe accurately. After 

 denying Robert Brown's assertion that 

 the pollen tubes of the orchids arise in 

 the ovary, Schleiden proceeded to 

 describe and figure the pollen tube as 

 penetrating not merely the style and 

 then the micropyle, but even far into 

 the embryo sac itself. 



Here, as he says in his Grundziige 

 (II., p. 373): 



"The end of the pollen tube soon 

 swells, either in such a way that the 

 vesicle arising in it fills the whole 

 cavity of the portion of the tube within 

 the embryo sac, or there is left, between 

 the apex of the embryo sac and the 

 embryonal vesicle of the tube, a long or 

 a short cylindrical portion of the latter, 

 the suspensor." 



He thus regarded the embryo sac as a 

 sort of hatching place for the embryo, 

 which he thought formed from the end 

 of the pollen tube. This idea of the 

 origin of the embryo really denied the 

 occurrence of any actual sexual process, 

 and made the pollen the mother of the 

 embryo. 



ORIGIN OF EMBRYO. 



In 1846, however, the error of this 

 conception was clearly demonstrated by 

 Amici, who showed that the embryo of 

 the orchids arises from an egg which is 

 alreadly present in the embryo sac 

 when the pollen tube reaches it. It is 

 this pre-existing egg, according to 

 Amici, that is stimulated to form the 

 embryo by the presence near it of the 

 pollen tube. This view was confidently 

 supported by Mohl (1847) and Hof- 

 meister (1847) in the following year, and 

 the controversy with vSchleiden became 

 even more spirited. As Mohl afterward 

 wrote (1863), men were "led astray by 

 their previous conceptions to believe 

 they saw what the}^ could not have 



seen." The dispute even approached 

 the acrimonious, as when Schleiden 

 (1843) says of one worker's figures. 



STAMENS AND PISTIL OF TOBACCO 

 FLOWER 



In the center rises the tall stigma with 

 its glossy, knob-like end, the pistil. 

 About it stand five stamens, the 

 anthers of which have already burst 

 open and released the light yellow 

 grains of pollen, which show in the 

 photograph as a brilUant white. 

 Photograph highly enlarged. (Fig. 5.) 



