916 



expanded cavity is closely lined with the membrane, a circumstance 

 in favour of the idea that the tube is only an extension from the nu- 

 cleus ; but in two instances, the tube did not expand at the cavity, 

 and seemed to be abortive insertions of the pollen-tube : these, con- 

 trary to the usual course, were filled with slightly coloured matter. 



The tubular lining of the neck of the ovule could not, at the time 

 of fecundation, be traced much below the expanded cavity, and the 

 embryo sac, when dissected away, appeared to be quite closed at the 

 top. If it be continuous with the tube, it is natural to expect that, 

 at its first appearance, a very slight pressure would cause the regres- 

 sion of the loose granular matter into the tube ; but this does not 

 occur ; and if there must be an inflation of the pollen-tube, after its 

 admission within the nucleus, we should rather expect to find it at 

 the point where the embryo sac is formed ; but, between that point 

 and the cavity in the neck of the ovule, there is, at the time of fecun- 

 dation, a sensible barrier of rather compact tissue, through which no 

 tubular passage could at any time be traced. For this reason, I still 

 hesitate to receive the theory of Schleider as being fully proved, though 

 I admit that the evidence in its favour is very much stronger than I 

 anticipated, and indeed all but conclusive ; for in a very short time 

 after the insertion of the tube within the nucleus (the time of fe- 

 cundation) the tube does appear to descend below the cavity ; so that 

 either its lower extremity comes into direct contact with the previ- 

 ously existing embryo-sac, or the extremity itself is inflated and con- 

 verted into an embryo-sac. It is difl3cult to say whether any amount 

 of skill in dissection will prove which of these interpretations is the 

 true one ; and it will be more practicable, and equally satisfactory, to 

 obtain dissections of the ovarium at the precise juncture when the 

 pollen-tube has reached the apex of the neck of the ovule, but has 

 not penetrated so far as the cavity at the base. To this point of the 

 inquiry I would therefore earnestly direct the attention of all who 

 may wish to pursue the subject. 



The subjoined figures are taken, in every case, from actual dissec- 

 tions. 



Fig. 1 . Section of ovule of a species of gourd, 1 times magnified, a. Diverg- 

 ing branches of stigraatic tissue, as seen in a transverse section of the 

 ovarium, b. Stigmatic tissue in contact with the apex of the ovule. 



Fi"'. 2. The same 40 times magnified, a. Site of the embryo-sac. b. Stigmatic 

 tissue in immediate contact with c, the apex of the ovule. 



Fig. 3. Another example of the same. 



Fig. 4. Apex of the primine, showing the foramen of the ovule. 



