SPERMATOPHYTES— GYMNOSPERMS 331 



After the embryos begin to grow down into the endosperm, oblong 

 pieces containing the embryos should be cut out. 



After the cotyledons appear, useful preparations may be made by 

 dissecting out the entire embryos, which may be fixed in chromo-acetic 

 acid, washed, stained in eosin or in Delafield's haematoxylin, placed in 

 10 per cent glycerin, and mounted by the Venetian turpentine method. 

 Since the suspensors become long and irregular, each embryo should 

 be placed in a separate dish, lest the suspensors become entangled and 

 broken. 



After the stony layer becomes hard, it is better to use a small fret 

 saw for opening the ovule. Before the embryo has pushed down into 

 the endosperm, the ovule should be sawed in two transversely. The 

 endosperm and nucellus can then be picked out and treated as desired. 

 After the tip of the embryo reaches the middle of the endosperm, the 

 ovule should be sawed open longitudinally. 



GYMNOSPERMS— GINKGOALES 



From the standpoint of technique the Ginkgoales, now represented 

 only by Ginkgo biloba, are less difficult than the Cycadales, but the 

 difficulties are somewhat similar. 



The vegetative structures. — The adult stem is harder to cut than 

 Pinus, but good sections should be secured by boiling in water for 24 

 hours, soaking in equal parts 95 per cent alcohol and glycerin for a 

 couple of weeks, and using the steam method. 



Transverse sections of the "spur" shoots are easily cut. They have 

 a comparatively large pith and narrow zone of wood, thus contrasting 

 sharply with a long shoot of the same diameter, which has a small pith 

 and wide zone of wood. 



The petiole of the leaf and the peduncle of the ovule look alike; 

 but transverse sections show two bundles in the petiole and four in the 

 peduncle. On this account, it is thought that the peduncle consists of 

 two petioles fused together, each bearing a blade (collar) with an 

 ovule. The fact that, in "abnormal" cases, the collar becomes leaflike, 

 is responsible for this interpretation. Both petiole and peduncle cut 

 easily in paraffin. 



Spermatogenesis. — The entire staminate cone, even at the time of 

 shedding pollen, can be cut in paraffin. For the latest stages, however, 

 it is better to remove the sporophylls and cut them separately, since 

 the sections must not be thicker than 5 yt, if they are to show the 

 internal structures of the pollen grain. 



