82 MAINS AGRICULTURAL EXPERIMENT STATION. 1904. 



attempt is made to reciprocally cross Matthiola annua and 

 Matthiola glabra, two closely related species. 1 



Thuret 3 is authority for the statement that Fucus vesiculosus 

 crossed by Fucus serratus is fertile, but that reciprocal crosses 

 with these plants cannot be made. Strasburger 2 found that 

 Orchis fusca pollen will stimulate the ovules of Orchis Morio 

 into normal activity, while pollen of Orchis Morio will not form 

 tubes on the stigma of Orchis fusca. 



Among more familiar plants, other supposed impossible recip- 

 rocals are the red currant and common garden tomato, and sum- 

 mer crookneck and bush scallop squashes. These cases will be 

 discussed in detail later in this paper. 



PROCESSES LEADING TO THE FORMATION OE SEED. 



In order to pave the way for a study of abnormal conditions, 

 it will be well at this point to review in a general way the normal 

 process of fertilization. 3 



It is now well known that the pollen grain, after being lodged 

 on the sticky surface of the stigma, undergoes a process similar 

 to that of the germination of spores of the lower orders of plants, 

 and not greatly unlike that of the germination of seeds. Soon 

 after the deposit of the pollen, the grains absorb moisture and 

 increase in size ; the outer wall, the extine, bursts, and inhibition 

 of watery solutions incites to activity the protoplasm of the 

 grain, and movements of cytoplasm within cause the extension 

 of the inner wall so as to form a tube, the so-called pollen tube. 

 Now the pollen tube, once started in its downward course, makes 

 its way through or between the parenchyma cells of the pistil, 

 manifesting its growth by the formation of new nuclei in the pro- 

 toplasm, and in the extension of the wall in the form of a tube. 

 This tube penetrates to the region of the ovules and when the 

 micropyle is reached the pollen nuclei pass into the embryo-sac, 

 and a union of the elements is effected which results in the form- 

 ation of seed. Germination when once started may be completed 

 in a few hours, as in the case of Cereus grandiUorus ; or it may 

 require several months, as in the case with orchids ; or almost a 

 year, as is true with the pines. 



1. Cited by A. R. Wallace, Darwinism, p. 155. 



2. Cited by H. P. Gould, Potency of Pollen, Cornell University Thesis, 1S97, p. 28. 



3. Cf. also, Rpt. Maine Agr. Expt. Sta., 1898, 219, et seq. 



