billings: embryo nutrition in labiate. 71 



cell (fig. 5). The haustorial nuclei vary usually from twenty 

 to thirty micromillimeters in diameter, but the smallest are 

 much larger than any formed in the endosperm tissue, since 

 these average only about five micromillimeters in diameter. 

 Another difference is the much greater size of the nucleoli of 

 the haustorial nuclei. In addition, the nucleoli are not vesicu- 

 lar, as are most of those in the endosperm tissue, but are solid. 

 The large size of the nucleoli would seem to indicate an in- 

 creased nutritive function on the part of the nucleus, especially 

 in light of the theory that nucleoli represent reserve food sub- 

 stance. There is no evidence that the haustorial nuclei undergo 

 division, either in Lamium or in the coenocytic haustoria of any 

 other of the Labiatsg investigated. There is some variance in 

 the explanations of the peculiarity of these nuclei, but dis- 

 cussion of them will be reserved till the close of the paper. 



The suspensor elongates during the growth of the embryo 

 sac and finally attains an unusual length (fig. 6). Its course 

 is for some time plainly visible in the haustorium and for a 

 longer time in endosperm tissue. The portion nearest the em- 

 bryo persists while the remainder slowly disintegrates. The 

 appearance of the suspensor is such that at no time does it 

 seem to serve as a conductor of food substances to the embryo, 

 at least from any locality other than that of the endosperm 

 tissue immediately surrounding it. It appears to have fulfilled 

 its function when it carried the embryo from the haustorium 

 down into the midst of developing endosperm tissue. 



While the micropylar haustorium is transferring materials 

 to one end of the endosperm tissue the opposite end is nour- 

 ished by substances conducted through a vascular bundle that 

 passes down the integument and terminates near the chalaza. 

 The little depression or pocket in which the antipodals undergo 

 disintegration is deepened until it forms a short canal, which 

 extends from the endosperm toward the terminus of the vas- 

 cular bundle. It does not merit the name of haustorium to the 

 extent that the micropylar expansion of the sac does, since it 

 exerts little or no absorptive influence ' upon the integument, 

 cells bordering it, but rather seems designed to facilitate con- 

 duction from the bundle. Its increase in length is not accom- 

 panied by a pronounced increase in diameter nor does it contain 

 nuclei. 



Later stages in ernbryo development show increase of the 



